Georgie and Mandy get upset when Audrey disciplines CeeCee without their permission.

Amy and Sheldon host a Valentine's Day edition of Fun With Flags; Penny and Leonard wrestle with getting older; Howard and Bernadette make a discovery in their hot tub; Raj is torn between Emily and another woman.

The gang celebrates news of Bernadette's pregnancy by singing karaoke; Wolowitz's reaction to the pregnancy announcement worries Bernadette; Wolowitz believes he needs to make more money to support his growing family.

When a relative passes away unexpectedly, the family must debate about who should gain custody of a jaded nephew, who is just shy of his 18th birthday.

Problems arise on Beverly Rose's first day of kindergarten; Becky and Darlene have a disagreement; Harris advises an unusual solution for Dan's back pain.

Davis is locked in a jail cell to raise money for charity; Wanda tries to install a toilet.

Karen prepares an eyewitness testimony; Hank tries becoming a rodeo clown.

Brent uses a drone to harass Oscar; Wanda and Emma attempt to measure the intelligence of turkeys.

Karen and Davis discover a mannequin dumped in the woods and try to solve the crime; at Corner Gas, Brent surprises Wanda with a scanner; in The Ruby, Lacey, Oscar, Hank, and Emma get drawn into an unusual bet about hand sanitizer.

Taxi passengers win money by answering trivia questions.

Taxi passengers win money by answering trivia questions.

Davis is locked in a jail cell to raise money for charity; Wanda tries to install a toilet.

Karen prepares an eyewitness testimony; Hank tries becoming a rodeo clown.

Brent uses a drone to harass Oscar; Wanda and Emma attempt to measure the intelligence of turkeys.

Karen and Davis discover a mannequin dumped in the woods and try to solve the crime; at Corner Gas, Brent surprises Wanda with a scanner; in The Ruby, Lacey, Oscar, Hank, and Emma get drawn into an unusual bet about hand sanitizer.

Taxi passengers win money by answering trivia questions.

Taxi passengers win money by answering trivia questions.

Davis is locked in a jail cell to raise money for charity; Wanda tries to install a toilet.

Karen prepares an eyewitness testimony; Hank tries becoming a rodeo clown.

Brent uses a drone to harass Oscar; Wanda and Emma attempt to measure the intelligence of turkeys.

Karen and Davis discover a mannequin dumped in the woods and try to solve the crime; at Corner Gas, Brent surprises Wanda with a scanner; in The Ruby, Lacey, Oscar, Hank, and Emma get drawn into an unusual bet about hand sanitizer.

Dan encourages the family to decorate the house for Halloween; Harris takes a stand on an issue that ruffles a few feathers in Darlene's new neighborhood.

While Monica helps Rachel move out, the two women have a war of words; Chandler says a "financial" adios to Joey.

Rachel regrets asking Phoebe to jog with her when her uncoordinated movements attract unwanted attention.

After bleaching his teeth, Ross discovers they glow in the dark; Joey's new roommate wants to redecorate.

Georgie and Mandy get upset when Audrey disciplines CeeCee without their permission.

For the first time in nine years, the gang celebrates Sheldon's birthday - surprising him with a special guest.

Leonard, Sheldon and Wolowitz file for a patent on their new invention; Penny, Amy and Bernadette give dating advice to Koothrappali after his breakup with Emily.

Sheldon makes a surprise revelation when Amy buys him a new laptop; Leonard and Wolowitz get sold out by Koothrappali after lying to their wives to attend a movie screening.

Dan encourages the family to decorate the house for Halloween; Harris takes a stand on an issue that ruffles a few feathers in Darlene's new neighborhood.

Darlene receives a promotion at her company, but she quickly learns the fancy title is not all it's cracked up to be; when Louise loses her job at Casita Bonita, an opportunity arises to work with Jackie at the Lunch Box.

Janine invites Joey, Monica and Ross to a TV taping; Phoebe and Rachel want an early glimpse at their Christmas gifts.

Janine's attitude causes strife between Joey and his friends; Rachel gets an apothecary table from a flea market.

Ross and Chandler argue over authorship of a joke; a question from Monica puts Phoebe on the spot; Joey reluctantly takes a job at Central Perk.

Rachel is worried about her sister's flirtation with Ross; sickly Monica is well enough to seduce Chandler; Joey uses free food to lure women to date him.

For the first time in nine years, the gang celebrates Sheldon's birthday - surprising him with a special guest.

Leonard, Sheldon and Wolowitz file for a patent on their new invention; Penny, Amy and Bernadette give dating advice to Koothrappali after his breakup with Emily.

Sheldon shares a secret about Leonard when the two go on a weekend trip with Penny and Amy; Koothrappali goes all out with pregnancy gifts.

During a group get-together, a minor argument between Sheldon and Leonard turns into a heated debate, leaving the rest of the gang to choose sides.

Sheldon makes a surprise revelation when Amy buys him a new laptop; Leonard and Wolowitz get sold out by Koothrappali after lying to their wives to attend a movie screening.

Darlene receives a promotion at her company, but she quickly learns the fancy title is not all it's cracked up to be; when Louise loses her job at Casita Bonita, an opportunity arises to work with Jackie at the Lunch Box.

For the first time in nine years, the gang celebrates Sheldon's birthday - surprising him with a special guest.

Leonard, Sheldon and Wolowitz file for a patent on their new invention; Penny, Amy and Bernadette give dating advice to Koothrappali after his breakup with Emily.

Sheldon shares a secret about Leonard when the two go on a weekend trip with Penny and Amy; Koothrappali goes all out with pregnancy gifts.

During a group get-together, a minor argument between Sheldon and Leonard turns into a heated debate, leaving the rest of the gang to choose sides.

Janine invites Joey, Monica and Ross to a TV taping; Phoebe and Rachel want an early glimpse at their Christmas gifts.

Janine's attitude causes strife between Joey and his friends; Rachel gets an apothecary table from a flea market.

Ross and Chandler argue over authorship of a joke; a question from Monica puts Phoebe on the spot; Joey reluctantly takes a job at Central Perk.

Rachel is worried about her sister's flirtation with Ross; sickly Monica is well enough to seduce Chandler; Joey uses free food to lure women to date him.

Sheldon shares a secret about Leonard when the two go on a weekend trip with Penny and Amy; Koothrappali goes all out with pregnancy gifts.

During a group get-together, a minor argument between Sheldon and Leonard turns into a heated debate, leaving the rest of the gang to choose sides.

Dan encourages the family to decorate the house for Halloween; Harris takes a stand on an issue that ruffles a few feathers in Darlene's new neighborhood.

Darlene receives a promotion at her company, but she quickly learns the fancy title is not all it's cracked up to be; when Louise loses her job at Casita Bonita, an opportunity arises to work with Jackie at the Lunch Box.

Brent talks Hank into starting a blog; Lacey's friend gets her own cooking show; Wanda helps Davis with his taxes.

Brent realizes that Corner Gas may not actually be within the town of Dog River.

Emma sees high art in Hank's hedge-trimming and sells his services around town; prompted by Oscar, Brent tries to collect on the IOUs piling up at Corner Gas, resorting to unorthodox means; Davis and Karen set up the cop shop in The Ruby.

When Wullerton's weekly paper goes under, the gang worries the Dog River Howler will too; Wanda and Emma set out to recruit new advertisers, while Brent helps Oscar start an online version that raises eyebrows; Karen befriends a crow.

Unassuming people enter a taxi cab as simple passengers taking a normal ride, only to be surprised when they discover that they're instant contestants; Adam Grove, asks the passengers trivia questions as he escorts them to their destination.

Unassuming people enter a taxi cab as simple passengers taking a normal ride, only to be surprised when they discover that they're instant contestants; Adam Grove, asks the passengers trivia questions as he escorts them to their destination.

Brent talks Hank into starting a blog; Lacey's friend gets her own cooking show; Wanda helps Davis with his taxes.

Brent realizes that Corner Gas may not actually be within the town of Dog River.

Emma sees high art in Hank's hedge-trimming and sells his services around town; prompted by Oscar, Brent tries to collect on the IOUs piling up at Corner Gas, resorting to unorthodox means; Davis and Karen set up the cop shop in The Ruby.

When Wullerton's weekly paper goes under, the gang worries the Dog River Howler will too; Wanda and Emma set out to recruit new advertisers, while Brent helps Oscar start an online version that raises eyebrows; Karen befriends a crow.

Unassuming people enter a taxi cab as simple passengers taking a normal ride, only to be surprised when they discover that they're instant contestants; Adam Grove, asks the passengers trivia questions as he escorts them to their destination.

Unassuming people enter a taxi cab as simple passengers taking a normal ride, only to be surprised when they discover that they're instant contestants; Adam Grove, asks the passengers trivia questions as he escorts them to their destination.

Brent talks Hank into starting a blog; Lacey's friend gets her own cooking show; Wanda helps Davis with his taxes.

Brent realizes that Corner Gas may not actually be within the town of Dog River.

Emma sees high art in Hank's hedge-trimming and sells his services around town; prompted by Oscar, Brent tries to collect on the IOUs piling up at Corner Gas, resorting to unorthodox means; Davis and Karen set up the cop shop in The Ruby.

When Wullerton's weekly paper goes under, the gang worries the Dog River Howler will too; Wanda and Emma set out to recruit new advertisers, while Brent helps Oscar start an online version that raises eyebrows; Karen befriends a crow.

Jackie must come to terms with her mother becoming ill; Darlene's job hunt proves to be more difficult than anticipated.

Janine invites Joey, Monica and Ross to a TV taping; Phoebe and Rachel want an early glimpse at their Christmas gifts.

Janine's attitude causes strife between Joey and his friends; Rachel gets an apothecary table from a flea market.

Ross and Chandler argue over authorship of a joke; a question from Monica puts Phoebe on the spot; Joey reluctantly takes a job at Central Perk.

Rachel is worried about her sister's flirtation with Ross; sickly Monica is well enough to seduce Chandler; Joey uses free food to lure women to date him.

A bad day compels Penny to re-evaluate her choices - including Leonard; Bernadette and Howard must care for Mrs. Wolowitz; Sheldon gives Raj advice on relationships.

Faced with an uncertain future, Sheldon considers a major change; Emily and Raj decide to take things to the next level.

Leonard and Amy make an unexpected trip to Arizona to fetch Sheldon; Penny interviews for a job at Bernadette's company; Stuart's relationship with Mrs. Wolowitz disturbs Howard.

Jackie must come to terms with her mother becoming ill; Darlene's job hunt proves to be more difficult than anticipated.

Darlene, Ben, Becky and Beverly Rose move into the new house, where Darlene implements a new set of rules.

Sheldon explores Germany behind Mary's back; Missy attempts to pull a fast one on George Sr.; Meemaw and Dale adjust to living together.

Missy steps up; Mary has a surprise for George; Sheldon finds his dorm occupied.

Leonard is happy to meet new neighbor Penny, but his roommate thinks he is chasing an impossible dream.

Leonard volunteers to sign for a package, hoping to make a good impression on Penny.

This holiday season, the Parkers discover that romance isn't always a smooth ride as Matt and Eve are on thin ice; Gabe enlists Riley to help Amelie impress his mom; Carter seeks help with his promposal.

With the threat of a nurse walkout, Alex is caught between her colleagues and Joyce; Ron and Bruce go above and beyond to help an unexpected patient.

Unhappy to learn that Penny is seeing someone, Leonard summons the courage to ask another woman on a date.

Getting fired gives Sheldon the opportunity to explore life beyond physics, but when he spends his time weaving ponchos and acting like a shut-in, Leonard calls Sheldon's mother for assistance.

Leonard, realizing his pursuit of Penny is fruitless, has an unexpected encounter with a fellow scientist (Sara Gilbert).

Penny sleeps on Leonard and Sheldon's couch when Wolowitz seduces her friend and takes over her apartment; in need of a fourth member, the guys ask Penny to join their "Halo" team.

Leonard is happy to meet new neighbor Penny, but his roommate thinks he is chasing an impossible dream.

Leonard volunteers to sign for a package, hoping to make a good impression on Penny.

Unhappy to learn that Penny is seeing someone, Leonard summons the courage to ask another woman on a date.

Getting fired gives Sheldon the opportunity to explore life beyond physics, but when he spends his time weaving ponchos and acting like a shut-in, Leonard calls Sheldon's mother for assistance.

Leonard, realizing his pursuit of Penny is fruitless, has an unexpected encounter with a fellow scientist (Sara Gilbert).

Penny sleeps on Leonard and Sheldon's couch when Wolowitz seduces her friend and takes over her apartment; in need of a fourth member, the guys ask Penny to join their "Halo" team.

Leonard is happy to meet new neighbor Penny, but his roommate thinks he is chasing an impossible dream.

Leonard volunteers to sign for a package, hoping to make a good impression on Penny.

Unhappy to learn that Penny is seeing someone, Leonard summons the courage to ask another woman on a date.

Getting fired gives Sheldon the opportunity to explore life beyond physics, but when he spends his time weaving ponchos and acting like a shut-in, Leonard calls Sheldon's mother for assistance.

Leonard, realizing his pursuit of Penny is fruitless, has an unexpected encounter with a fellow scientist (Sara Gilbert).

Penny sleeps on Leonard and Sheldon's couch when Wolowitz seduces her friend and takes over her apartment; in need of a fourth member, the guys ask Penny to join their "Halo" team.

On a blind date, Koothrappali discovers that he can talk to the opposite sex after a few drinks, but his date takes an interest in Sheldon.

Penny tries to mediate when Sheldon and Leonard disagree on whether to present their joint findings at a physics conference.

Leonard and Sheldon try to avoid seeing Penny perform after hearing her sing, but the elaborate lie Sheldon tells leads to an unexpected result.

Leonard and the boys avoid Sheldon when he gets sick, leaving Penny to nurse him back to health.

Sheldon and Leonard look for a way to derail a 15-year-old physics prodigy's research.

When Sheldon tries to prove his mental superiority as they train for the Physics Bowl, the guys kick him off the team and bring his nemesis (Sara Gilbert) aboard.

Leonard and the guys buy a time machine prop from a classic movie; Penny tells the guys their obsession with comics and toys is pathetic.

Leonard devises a plan to eliminate his rivals when he, Wolowitz and Koothrappali all fall for Sheldon's twin sister, but his plan backfires when Sheldon decides to choose who his sister dates.

Penny learns that Leonard does not celebrate birthdays, so she plans a surprise party; Sheldon unexpectedly gets to live out one of his biggest fantasies in an electronics store.

When Leonard finally works up the courage to ask Penny out on a date, they each turn to Sheldon for advice.

Penny's first date with Leonard goes awry; Penny finds Sheldon to be an unwilling confidant.

After seeing Penny with a handsome new guy, Leonard rushes into a rebound relationship with Sheldon's nemesis, Leslie Winkle.

Sheldon creates a monster when he introduces Penny to online gaming.

Raj gets an inflated ego and makes a play for Penny after being referenced in a magazine article.

Leonard and his friends stage an intervention to force Sheldon to face his fear of driving.

Sheldon and the gang are confused when a young grad student is attracted to him.

On a blind date, Koothrappali discovers that he can talk to the opposite sex after a few drinks, but his date takes an interest in Sheldon.

Penny tries to mediate when Sheldon and Leonard disagree on whether to present their joint findings at a physics conference.

Leonard and Sheldon try to avoid seeing Penny perform after hearing her sing, but the elaborate lie Sheldon tells leads to an unexpected result.

Leonard and the boys avoid Sheldon when he gets sick, leaving Penny to nurse him back to health.

Sheldon and Leonard look for a way to derail a 15-year-old physics prodigy's research.

When Sheldon tries to prove his mental superiority as they train for the Physics Bowl, the guys kick him off the team and bring his nemesis (Sara Gilbert) aboard.

Leonard and the guys buy a time machine prop from a classic movie; Penny tells the guys their obsession with comics and toys is pathetic.

Leonard devises a plan to eliminate his rivals when he, Wolowitz and Koothrappali all fall for Sheldon's twin sister, but his plan backfires when Sheldon decides to choose who his sister dates.

Penny learns that Leonard does not celebrate birthdays, so she plans a surprise party; Sheldon unexpectedly gets to live out one of his biggest fantasies in an electronics store.

When Leonard finally works up the courage to ask Penny out on a date, they each turn to Sheldon for advice.

Penny's first date with Leonard goes awry; Penny finds Sheldon to be an unwilling confidant.

After seeing Penny with a handsome new guy, Leonard rushes into a rebound relationship with Sheldon's nemesis, Leslie Winkle.

Georgie's feud with a rival store threatens his partnership with Ruben; Mandy finds out Georgie's been keeping secrets from her.

Georgie and Mandy struggle to balance work, family and the holidays when Audrey plans an unexpected Christmas vacation.

Leonard and his friends stage an intervention to force Sheldon to face his fear of driving.

Sheldon and the gang are confused when a young grad student is attracted to him.

On a blind date, Koothrappali discovers that he can talk to the opposite sex after a few drinks, but his date takes an interest in Sheldon.

Penny tries to mediate when Sheldon and Leonard disagree on whether to present their joint findings at a physics conference.

Leonard and Sheldon try to avoid seeing Penny perform after hearing her sing, but the elaborate lie Sheldon tells leads to an unexpected result.

Leonard and the boys avoid Sheldon when he gets sick, leaving Penny to nurse him back to health.

Sheldon and Leonard look for a way to derail a 15-year-old physics prodigy's research.

When Sheldon tries to prove his mental superiority as they train for the Physics Bowl, the guys kick him off the team and bring his nemesis (Sara Gilbert) aboard.

Leonard and the guys buy a time machine prop from a classic movie; Penny tells the guys their obsession with comics and toys is pathetic.

Leonard devises a plan to eliminate his rivals when he, Wolowitz and Koothrappali all fall for Sheldon's twin sister, but his plan backfires when Sheldon decides to choose who his sister dates.

Penny learns that Leonard does not celebrate birthdays, so she plans a surprise party; Sheldon unexpectedly gets to live out one of his biggest fantasies in an electronics store.

When Leonard finally works up the courage to ask Penny out on a date, they each turn to Sheldon for advice.

Penny's first date with Leonard goes awry; Penny finds Sheldon to be an unwilling confidant.

After seeing Penny with a handsome new guy, Leonard rushes into a rebound relationship with Sheldon's nemesis, Leslie Winkle.

Sheldon creates a monster when he introduces Penny to online gaming.

Raj gets an inflated ego and makes a play for Penny after being referenced in a magazine article.

Leonard and his friends stage an intervention to force Sheldon to face his fear of driving.

Sheldon and the gang are confused when a young grad student is attracted to him.

When Sheldon bans Penny from the apartment for a series of petty infractions, Penny vows to get revenge.

Leonard inadvertently steals away the new woman Wolowitz thinks is the love of his life.

Sheldon is thrilled when Leonard starts dating a woman who meets Sheldon's stringent standards.

Leonard asks Penny for advice when his new relationship starts moving too fast.

Penny starts dating Leonard's handsome colleague; Leonard and his friends are tortured by Sheldon's obsession with gift-giving etiquette.

When Penny's comment about Wolowitz's love life sends him into a depressed stupor, his friends lose their most important teammate in an upcoming fighting-robot competition.

Sheldon develops a scientific procedure for making friends; Kripke controls a new supercomputer.

Sheldon's solution to Penny's financial difficulty leads to a confrontation between Leonard and Penny's ex-boyfriend.

Leonard and Penny are drawn together after a disastrous visit from Leonard's mother (Christine Baranski).

A paintball game leads to a fight between Sheldon and Penny, and romance for Leslie and Wolowitz.

Leonard, Sheldon and Wolowitz are ecstatic to learn that a famous science-fiction actress (Summer Glau) is aboard the train they are taking to San Francisco.

Penny's home business turns into a complete nightmare when Sheldon takes over.

Penny develops a rivalry with a sexy new female neighbor who threatens her position as queen bee of the building.

Wolowitz and Leonard decide to check out a local bar on Ladies' Night.

Koothrappali and Leonard take Wolowitz to Las Vegas; Sheldon is forced to bunk with Penny when he gets locked out of his apartment.

Penny makes a surprising revelation about Leonard while on her date with Stuart; Wolowitz finds a critical design flaw in his NASA project.

When Sheldon bans Penny from the apartment for a series of petty infractions, Penny vows to get revenge.

Leonard inadvertently steals away the new woman Wolowitz thinks is the love of his life.

Sheldon is thrilled when Leonard starts dating a woman who meets Sheldon's stringent standards.

Leonard asks Penny for advice when his new relationship starts moving too fast.

Penny starts dating Leonard's handsome colleague; Leonard and his friends are tortured by Sheldon's obsession with gift-giving etiquette.

When Penny's comment about Wolowitz's love life sends him into a depressed stupor, his friends lose their most important teammate in an upcoming fighting-robot competition.

Sheldon develops a scientific procedure for making friends; Kripke controls a new supercomputer.

Sheldon's solution to Penny's financial difficulty leads to a confrontation between Leonard and Penny's ex-boyfriend.

Leonard and Penny are drawn together after a disastrous visit from Leonard's mother (Christine Baranski).

A paintball game leads to a fight between Sheldon and Penny, and romance for Leslie and Wolowitz.

Leonard, Sheldon and Wolowitz are ecstatic to learn that a famous science-fiction actress (Summer Glau) is aboard the train they are taking to San Francisco.

Penny's home business turns into a complete nightmare when Sheldon takes over.

Penny develops a rivalry with a sexy new female neighbor who threatens her position as queen bee of the building.

Wolowitz and Leonard decide to check out a local bar on Ladies' Night.

Koothrappali and Leonard take Wolowitz to Las Vegas; Sheldon is forced to bunk with Penny when he gets locked out of his apartment.

Penny makes a surprising revelation about Leonard while on her date with Stuart; Wolowitz finds a critical design flaw in his NASA project.

When Sheldon bans Penny from the apartment for a series of petty infractions, Penny vows to get revenge.

Leonard inadvertently steals away the new woman Wolowitz thinks is the love of his life.

Sheldon is thrilled when Leonard starts dating a woman who meets Sheldon's stringent standards.

Leonard asks Penny for advice when his new relationship starts moving too fast.

Penny starts dating Leonard's handsome colleague; Leonard and his friends are tortured by Sheldon's obsession with gift-giving etiquette.

When Penny's comment about Wolowitz's love life sends him into a depressed stupor, his friends lose their most important teammate in an upcoming fighting-robot competition.

Sheldon develops a scientific procedure for making friends; Kripke controls a new supercomputer.

Sheldon's solution to Penny's financial difficulty leads to a confrontation between Leonard and Penny's ex-boyfriend.

Leonard and Penny are drawn together after a disastrous visit from Leonard's mother (Christine Baranski).

A paintball game leads to a fight between Sheldon and Penny, and romance for Leslie and Wolowitz.

Leonard, Sheldon and Wolowitz are ecstatic to learn that a famous science-fiction actress (Summer Glau) is aboard the train they are taking to San Francisco.

Penny's home business turns into a complete nightmare when Sheldon takes over.

Penny develops a rivalry with a sexy new female neighbor who threatens her position as queen bee of the building.

Wolowitz and Leonard decide to check out a local bar on Ladies' Night.

Koothrappali and Leonard take Wolowitz to Las Vegas; Sheldon is forced to bunk with Penny when he gets locked out of his apartment.

Penny makes a surprising revelation about Leonard while on her date with Stuart; Wolowitz finds a critical design flaw in his NASA project.

While Leonard prepares for a three-month science expedition, he and Penny re-evaluate their feelings for each other.

After tampering with Sheldon's Arctic-expedition data, the guys follow him back to Texas, which threatens Leonard's chances for romance with Penny.

Penny and Leonard try to recover from an awkward hookup; Howard and Sheldon make a high-stakes bet.

Howard and Raj hit a Goth nightclub to meet women; Sheldon tries chocolate-based behavior modification on Penny.

Raj faces deportation if he does not find a job; Leonard and Penny deal with Howard as a third wheel.

Sheldon seeks revenge on his nemesis, Wil Wheaton; Wolowitz wants Penny to set him up with one of her friends.

Sheldon teaches Leonard how to understand football; a kite-fighting incident threatens Howard and Raj's friendship.

Sheldon tries to make peace when Leonard and Penny get into an argument.

Penny is forced to rely on Sheldon when she is injured while Howard, Leonard and Raj are away.

After being humiliated on the radio, Sheldon vows to destroy Kripke; Wolowitz tries to not ruin his new relationship with Bernadette.

Sheldon tries to help Penny understand Leonard's work; Wolowitz gets jealous when Leonard starts hanging out with his new girlfriend.

Leonard is horrified when his mother (Christine Baranski) visits.

Sheldon and Koothrappali attend a university mixer; Leonard discovers that Penny believes in psychics.

After their apartment is robbed, Leonard and Sheldon turn to their friends to create a state-of-the-art security system.

Sheldon tries to figure out the answer to a physics problem by working with Penny.

Leonard must choose who to bring with him when he goes to see the Large Hadron Collider on Valentine's Day.

While Leonard prepares for a three-month science expedition, he and Penny re-evaluate their feelings for each other.

After tampering with Sheldon's Arctic-expedition data, the guys follow him back to Texas, which threatens Leonard's chances for romance with Penny.

Penny and Leonard try to recover from an awkward hookup; Howard and Sheldon make a high-stakes bet.

Howard and Raj hit a Goth nightclub to meet women; Sheldon tries chocolate-based behavior modification on Penny.

Raj faces deportation if he does not find a job; Leonard and Penny deal with Howard as a third wheel.

Sheldon seeks revenge on his nemesis, Wil Wheaton; Wolowitz wants Penny to set him up with one of her friends.

Sheldon teaches Leonard how to understand football; a kite-fighting incident threatens Howard and Raj's friendship.

Sheldon tries to make peace when Leonard and Penny get into an argument.

Penny is forced to rely on Sheldon when she is injured while Howard, Leonard and Raj are away.

After being humiliated on the radio, Sheldon vows to destroy Kripke; Wolowitz tries to not ruin his new relationship with Bernadette.

Sheldon tries to help Penny understand Leonard's work; Wolowitz gets jealous when Leonard starts hanging out with his new girlfriend.

Leonard is horrified when his mother (Christine Baranski) visits.

Sheldon and Koothrappali attend a university mixer; Leonard discovers that Penny believes in psychics.

After their apartment is robbed, Leonard and Sheldon turn to their friends to create a state-of-the-art security system.

Sheldon tries to figure out the answer to a physics problem by working with Penny.

Leonard must choose who to bring with him when he goes to see the Large Hadron Collider on Valentine's Day.

While Leonard prepares for a three-month science expedition, he and Penny re-evaluate their feelings for each other.

After tampering with Sheldon's Arctic-expedition data, the guys follow him back to Texas, which threatens Leonard's chances for romance with Penny.

Penny and Leonard try to recover from an awkward hookup; Howard and Sheldon make a high-stakes bet.

Howard and Raj hit a Goth nightclub to meet women; Sheldon tries chocolate-based behavior modification on Penny.

Raj faces deportation if he does not find a job; Leonard and Penny deal with Howard as a third wheel.

Sheldon seeks revenge on his nemesis, Wil Wheaton; Wolowitz wants Penny to set him up with one of her friends.

Sheldon teaches Leonard how to understand football; a kite-fighting incident threatens Howard and Raj's friendship.

Sheldon tries to make peace when Leonard and Penny get into an argument.

Penny is forced to rely on Sheldon when she is injured while Howard, Leonard and Raj are away.

After being humiliated on the radio, Sheldon vows to destroy Kripke; Wolowitz tries to not ruin his new relationship with Bernadette.

Sheldon tries to help Penny understand Leonard's work; Wolowitz gets jealous when Leonard starts hanging out with his new girlfriend.

Leonard is horrified when his mother (Christine Baranski) visits.

Sheldon and Koothrappali attend a university mixer; Leonard discovers that Penny believes in psychics.

After their apartment is robbed, Leonard and Sheldon turn to their friends to create a state-of-the-art security system.

Sheldon tries to figure out the answer to a physics problem by working with Penny.

Leonard must choose who to bring with him when he goes to see the Large Hadron Collider on Valentine's Day.

Sheldon ends up in traffic court after getting a ticket because of Penny.

When the guys buy a ring from "The Lord of the Rings" at a garage sale, the item threatens to tear them apart.

Sheldon's stage fright stands between him and a coveted award.

Penny and Leonard have a fight that threatens their relationship; Sheldon and Wil Wheaton face off once again.

Sheldon goes to extremes to keep Leonard and Penny happy when they stop speaking to each other.

Sheldon invites a famous physicist to the apartment, and competes with Leonard for her attention.

Leonard tells Penny about how he met Sheldon and what happened to the elevator.

Raj and Howard set up an online dating profile for Sheldon and find the perfect woman.

Penny tags along on Sheldon's first date; Wolowitz finds a new use for a robotic arm.

Realizing he will not live long enough to download his consciousness into a robot body, Sheldon tries to extend his life span.

When Sheldon searches for an alternative to human companionship, the guys become concerned.

An embarrassing secret of Wolowitz's is revealed; Raj and Sheldon get into a war at work.

Leonard realizes he is the only one in his group without a girlfriend; Sheldon wants to get rid of his girlfriend.

Leonard keeps an affair a secret from Sheldon, Howard and Raj.

Sheldon's interview with the FBI jeopardizes Wolowitz's security clearance.

While the guys camp out for a long-awaited movie screening, Penny and Bernadette invite Amy to her first slumber party.

Sheldon ends up in traffic court after getting a ticket because of Penny.

When the guys buy a ring from "The Lord of the Rings" at a garage sale, the item threatens to tear them apart.

Sheldon's stage fright stands between him and a coveted award.

Penny and Leonard have a fight that threatens their relationship; Sheldon and Wil Wheaton face off once again.

Sheldon goes to extremes to keep Leonard and Penny happy when they stop speaking to each other.

Sheldon invites a famous physicist to the apartment, and competes with Leonard for her attention.

Leonard tells Penny about how he met Sheldon and what happened to the elevator.

Raj and Howard set up an online dating profile for Sheldon and find the perfect woman.

Penny tags along on Sheldon's first date; Wolowitz finds a new use for a robotic arm.

Realizing he will not live long enough to download his consciousness into a robot body, Sheldon tries to extend his life span.

When Sheldon searches for an alternative to human companionship, the guys become concerned.

An embarrassing secret of Wolowitz's is revealed; Raj and Sheldon get into a war at work.

Leonard realizes he is the only one in his group without a girlfriend; Sheldon wants to get rid of his girlfriend.

Leonard keeps an affair a secret from Sheldon, Howard and Raj.

Sheldon's interview with the FBI jeopardizes Wolowitz's security clearance.

While the guys camp out for a long-awaited movie screening, Penny and Bernadette invite Amy to her first slumber party.

Sheldon ends up in traffic court after getting a ticket because of Penny.

When the guys buy a ring from "The Lord of the Rings" at a garage sale, the item threatens to tear them apart.

Sheldon's stage fright stands between him and a coveted award.

Penny and Leonard have a fight that threatens their relationship; Sheldon and Wil Wheaton face off once again.

Sheldon goes to extremes to keep Leonard and Penny happy when they stop speaking to each other.

Sheldon invites a famous physicist to the apartment, and competes with Leonard for her attention.

Leonard tells Penny about how he met Sheldon and what happened to the elevator.

Raj and Howard set up an online dating profile for Sheldon and find the perfect woman.

Penny tags along on Sheldon's first date; Wolowitz finds a new use for a robotic arm.

Realizing he will not live long enough to download his consciousness into a robot body, Sheldon tries to extend his life span.

When Sheldon searches for an alternative to human companionship, the guys become concerned.

An embarrassing secret of Wolowitz's is revealed; Raj and Sheldon get into a war at work.

Leonard realizes he is the only one in his group without a girlfriend; Sheldon wants to get rid of his girlfriend.

Leonard keeps an affair a secret from Sheldon, Howard and Raj.

Sheldon's interview with the FBI jeopardizes Wolowitz's security clearance.

While the guys camp out for a long-awaited movie screening, Penny and Bernadette invite Amy to her first slumber party.

Penny asks Leonard to lie to her father (Keith Carradine); Howard, Raj and Bernadette pull an all-nighter at a telescope.

Amy realizes she has feelings for Penny's ex; Koothrappali and Wolowitz try to prove who would be a better superhero.

The guys try to bond with Penny's new boyfriend through a costume contest.

Leonard's idea for a smartphone application causes friction in his friendship with Sheldon.

Bernadette runs into her ex-boyfriend (Rick Fox) while attending a science event with Wolowitz.

Sheldon takes acting lessons from Penny in hope of becoming a better teacher; Koothrappali fantasizes about his friend's girlfriend.

A wealthy donor makes Leonard question what he is willing to do for science.

Wolowitz considers taking things with Bernadette to the next level; Leonard and Raj's sister rekindle their relationship.

Sheldon is upset when he realizes Leonard is the center of their group of friends.

Leonard has to choose between Penny and his new girlfriend, Priya; Howard's magic trick drives Sheldon crazy.

The guys try to figure out who hacked Sheldon's online-game account.

Amy and Sheldon spread gossip as part of an experiment; Howard decides to take a big step in his relationship with Bernadette.

Priya dissects the roommate agreement; the ladies take Sheldon dancing.

Raj tries to cure his social anxiety; Penny spies on Leonard and his girlfriend through Bernadette.

Howard's mom winds up in the hospital after hearing news of her son's engagement to Bernadette.

Bernadette gets her Ph.D., inspiring the guys to tease Wolowitz about his lack of a doctorate; Raj becomes Sheldon's roommate.

Penny asks Leonard to lie to her father (Keith Carradine); Howard, Raj and Bernadette pull an all-nighter at a telescope.

Amy realizes she has feelings for Penny's ex; Koothrappali and Wolowitz try to prove who would be a better superhero.

The guys try to bond with Penny's new boyfriend through a costume contest.

Leonard's idea for a smartphone application causes friction in his friendship with Sheldon.

Bernadette runs into her ex-boyfriend (Rick Fox) while attending a science event with Wolowitz.

Sheldon takes acting lessons from Penny in hope of becoming a better teacher; Koothrappali fantasizes about his friend's girlfriend.

A wealthy donor makes Leonard question what he is willing to do for science.

Wolowitz considers taking things with Bernadette to the next level; Leonard and Raj's sister rekindle their relationship.

Sheldon is upset when he realizes Leonard is the center of their group of friends.

Leonard has to choose between Penny and his new girlfriend, Priya; Howard's magic trick drives Sheldon crazy.

The guys try to figure out who hacked Sheldon's online-game account.

Amy and Sheldon spread gossip as part of an experiment; Howard decides to take a big step in his relationship with Bernadette.

Priya dissects the roommate agreement; the ladies take Sheldon dancing.

Raj tries to cure his social anxiety; Penny spies on Leonard and his girlfriend through Bernadette.

Howard's mom winds up in the hospital after hearing news of her son's engagement to Bernadette.

Bernadette gets her Ph.D., inspiring the guys to tease Wolowitz about his lack of a doctorate; Raj becomes Sheldon's roommate.

Penny asks Leonard to lie to her father (Keith Carradine); Howard, Raj and Bernadette pull an all-nighter at a telescope.

Amy realizes she has feelings for Penny's ex; Koothrappali and Wolowitz try to prove who would be a better superhero.

The guys try to bond with Penny's new boyfriend through a costume contest.

Leonard's idea for a smartphone application causes friction in his friendship with Sheldon.

Bernadette runs into her ex-boyfriend (Rick Fox) while attending a science event with Wolowitz.

Sheldon takes acting lessons from Penny in hope of becoming a better teacher; Koothrappali fantasizes about his friend's girlfriend.

A wealthy donor makes Leonard question what he is willing to do for science.

Wolowitz considers taking things with Bernadette to the next level; Leonard and Raj's sister rekindle their relationship.

Sheldon is upset when he realizes Leonard is the center of their group of friends.

Leonard has to choose between Penny and his new girlfriend, Priya; Howard's magic trick drives Sheldon crazy.

The guys try to figure out who hacked Sheldon's online-game account.

Amy and Sheldon spread gossip as part of an experiment; Howard decides to take a big step in his relationship with Bernadette.

Priya dissects the roommate agreement; the ladies take Sheldon dancing.

Raj tries to cure his social anxiety; Penny spies on Leonard and his girlfriend through Bernadette.

Howard's mom winds up in the hospital after hearing news of her son's engagement to Bernadette.

Bernadette gets her Ph.D., inspiring the guys to tease Wolowitz about his lack of a doctorate; Raj becomes Sheldon's roommate.

Penny worries that she has ruined her relationship with her friends; Sheldon takes over the paintball team.

Amy is caught in the middle when Penny and Sheldon get into an argument over a pre-owned chair; Leonard tries to make his long-distance relationship more exciting.

Amy and Leonard try to become better acquainted; Bernadette, Howard and Mrs. Wolowitz spend the weekend together.

Raj wants a girlfriend, so Penny introduces him to a woman he can communicate with.

Wil Wheaton invites Leonard and Sheldon to a party at his house; Howard receives an opportunity.

Sheldon finds himself competing with the gang for his mother's (Laurie Metcalf) attention when she visits.

An attractive comic book artist tests Leonard and Priya's relationship; Sheldon tries to scare his friends.

Amy is devastated when Penny and Bernadette shop for wedding dresses without her.

Leonard and Penny spend time alone; Sheldon tries to face his fear of birds.

Sheldon is jealous when Stuart (Kevin Sussman), a guy from the comic book store, asks Amy out on a date.

Leonard must face the bully who targeted him in high school; Penny confronts her past actions.

Amy is upset with Sheldon when he isn't impressed with her recent accomplishment; Howard struggles with Bernadette's aversion to children.

Everything could change when Leonard spontaneously invites Penny to a romantic dinner.

Penny and Leonard experiment with their new relationship; Raj forms a bond with his phone's virtual assistant.

Leonard starts to reconsider his friendship with Sheldon; Wolowitz tries to choose his astronaut nickname.

Sheldon goes to work with Amy in her neurobiology lab when the university forces him to take a vacation; Bernadette asks Howard to sign a pre-nup.

Penny worries that she has ruined her relationship with her friends; Sheldon takes over the paintball team.

Amy is caught in the middle when Penny and Sheldon get into an argument over a pre-owned chair; Leonard tries to make his long-distance relationship more exciting.

Amy and Leonard try to become better acquainted; Bernadette, Howard and Mrs. Wolowitz spend the weekend together.

Raj wants a girlfriend, so Penny introduces him to a woman he can communicate with.

Wil Wheaton invites Leonard and Sheldon to a party at his house; Howard receives an opportunity.

Sheldon finds himself competing with the gang for his mother's (Laurie Metcalf) attention when she visits.

An attractive comic book artist tests Leonard and Priya's relationship; Sheldon tries to scare his friends.

Amy is devastated when Penny and Bernadette shop for wedding dresses without her.

Leonard and Penny spend time alone; Sheldon tries to face his fear of birds.

Sheldon is jealous when Stuart (Kevin Sussman), a guy from the comic book store, asks Amy out on a date.

Leonard must face the bully who targeted him in high school; Penny confronts her past actions.

Amy is upset with Sheldon when he isn't impressed with her recent accomplishment; Howard struggles with Bernadette's aversion to children.

Everything could change when Leonard spontaneously invites Penny to a romantic dinner.

Penny and Leonard experiment with their new relationship; Raj forms a bond with his phone's virtual assistant.

Leonard starts to reconsider his friendship with Sheldon; Wolowitz tries to choose his astronaut nickname.

Sheldon goes to work with Amy in her neurobiology lab when the university forces him to take a vacation; Bernadette asks Howard to sign a pre-nup.

Penny worries that she has ruined her relationship with her friends; Sheldon takes over the paintball team.

Amy is caught in the middle when Penny and Sheldon get into an argument over a pre-owned chair; Leonard tries to make his long-distance relationship more exciting.

Amy and Leonard try to become better acquainted; Bernadette, Howard and Mrs. Wolowitz spend the weekend together.

Raj wants a girlfriend, so Penny introduces him to a woman he can communicate with.

Wil Wheaton invites Leonard and Sheldon to a party at his house; Howard receives an opportunity.

Sheldon finds himself competing with the gang for his mother's (Laurie Metcalf) attention when she visits.

An attractive comic book artist tests Leonard and Priya's relationship; Sheldon tries to scare his friends.

Amy is devastated when Penny and Bernadette shop for wedding dresses without her.

Leonard and Penny spend time alone; Sheldon tries to face his fear of birds.

Sheldon is jealous when Stuart (Kevin Sussman), a guy from the comic book store, asks Amy out on a date.

Leonard must face the bully who targeted him in high school; Penny confronts her past actions.

Amy is upset with Sheldon when he isn't impressed with her recent accomplishment; Howard struggles with Bernadette's aversion to children.

Everything could change when Leonard spontaneously invites Penny to a romantic dinner.

Penny and Leonard experiment with their new relationship; Raj forms a bond with his phone's virtual assistant.

Leonard starts to reconsider his friendship with Sheldon; Wolowitz tries to choose his astronaut nickname.

Sheldon goes to work with Amy in her neurobiology lab when the university forces him to take a vacation; Bernadette asks Howard to sign a pre-nup.

Sheldon and his nemesis, Kripke, compete for a corner office; Penny feels uncomfortable after receiving a gift from Amy.

Sheldon's routine is turned upside down when his barber gets sick; Wolowitz questions his decision to go into space.

Sheldon chooses to participate in a guys-only weekend Star Wars gaming marathon rather than go with Amy to her aunt's birthday party; he gets a lesson from Penny and Amy.

When Penny buys Leonard and Sheldon "Star Trek" collectibles, Sheldon finds himself haunted by Mr. Spock; after a blind date, Raj believes he has met his future wife.

When Stephen Hawking comes to lecture at the university for a week, Wolowitz is given the task of maintaining his wheelchair, making Sheldon green with envy.

Knowledge of Howard's sexual history makes Bernadette reconsider their future together.

Wedding plans are jeopardized when NASA reschedules Howard's mission; Leonard says something in the bedroom that surprises Penny.

The gang tries to help Wolowitz and Bernadette get married before the space launch.

Raj faces his loneliness when his friends are out on dates; while in space, Wolowitz gets drawn into a fight between Bernadette and his mom.

Sheldon tries to intervene when he learns that Penny is thinking about breaking up with Leonard; Howard is picked on in space by the other astronauts.

Amy feels threatened by Sheldon's new assistant; Wolowitz starts to feel the pressures of being in space.

Wolowitz's return from space isn't all he expected; game night becomes a gender war.

The gang heads to Stuart's comic book store to celebrate Halloween; Leonard uses science to seduce Penny.

A game threatens Sheldon's relationship with Stephen Hawking; Penny secretly signs up for a college class.

Bernadette wants Wolowitz to move out of his mom's house; Sheldon is caught in the middle of Amy and Wil Wheaton's argument.

Raj and Howard try to figure out why Sheldon disappears at 2:45 every afternoon; jealousy arises in Penny and Leonard's relationship.

Sheldon and his nemesis, Kripke, compete for a corner office; Penny feels uncomfortable after receiving a gift from Amy.

Sheldon's routine is turned upside down when his barber gets sick; Wolowitz questions his decision to go into space.

Sheldon chooses to participate in a guys-only weekend Star Wars gaming marathon rather than go with Amy to her aunt's birthday party; he gets a lesson from Penny and Amy.

When Penny buys Leonard and Sheldon "Star Trek" collectibles, Sheldon finds himself haunted by Mr. Spock; after a blind date, Raj believes he has met his future wife.

When Stephen Hawking comes to lecture at the university for a week, Wolowitz is given the task of maintaining his wheelchair, making Sheldon green with envy.

Knowledge of Howard's sexual history makes Bernadette reconsider their future together.

Wedding plans are jeopardized when NASA reschedules Howard's mission; Leonard says something in the bedroom that surprises Penny.

The gang tries to help Wolowitz and Bernadette get married before the space launch.

Raj faces his loneliness when his friends are out on dates; while in space, Wolowitz gets drawn into a fight between Bernadette and his mom.

Sheldon tries to intervene when he learns that Penny is thinking about breaking up with Leonard; Howard is picked on in space by the other astronauts.

Amy feels threatened by Sheldon's new assistant; Wolowitz starts to feel the pressures of being in space.

Wolowitz's return from space isn't all he expected; game night becomes a gender war.

The gang heads to Stuart's comic book store to celebrate Halloween; Leonard uses science to seduce Penny.

A game threatens Sheldon's relationship with Stephen Hawking; Penny secretly signs up for a college class.

Bernadette wants Wolowitz to move out of his mom's house; Sheldon is caught in the middle of Amy and Wil Wheaton's argument.

Raj and Howard try to figure out why Sheldon disappears at 2:45 every afternoon; jealousy arises in Penny and Leonard's relationship.

Sheldon and his nemesis, Kripke, compete for a corner office; Penny feels uncomfortable after receiving a gift from Amy.

Sheldon's routine is turned upside down when his barber gets sick; Wolowitz questions his decision to go into space.

Sheldon chooses to participate in a guys-only weekend Star Wars gaming marathon rather than go with Amy to her aunt's birthday party; he gets a lesson from Penny and Amy.

When Penny buys Leonard and Sheldon "Star Trek" collectibles, Sheldon finds himself haunted by Mr. Spock; after a blind date, Raj believes he has met his future wife.

When Stephen Hawking comes to lecture at the university for a week, Wolowitz is given the task of maintaining his wheelchair, making Sheldon green with envy.

Knowledge of Howard's sexual history makes Bernadette reconsider their future together.

Wedding plans are jeopardized when NASA reschedules Howard's mission; Leonard says something in the bedroom that surprises Penny.

The gang tries to help Wolowitz and Bernadette get married before the space launch.

Raj faces his loneliness when his friends are out on dates; while in space, Wolowitz gets drawn into a fight between Bernadette and his mom.

Sheldon tries to intervene when he learns that Penny is thinking about breaking up with Leonard; Howard is picked on in space by the other astronauts.

Amy feels threatened by Sheldon's new assistant; Wolowitz starts to feel the pressures of being in space.

Wolowitz's return from space isn't all he expected; game night becomes a gender war.

The gang heads to Stuart's comic book store to celebrate Halloween; Leonard uses science to seduce Penny.

A game threatens Sheldon's relationship with Stephen Hawking; Penny secretly signs up for a college class.

Bernadette wants Wolowitz to move out of his mom's house; Sheldon is caught in the middle of Amy and Wil Wheaton's argument.

Raj and Howard try to figure out why Sheldon disappears at 2:45 every afternoon; jealousy arises in Penny and Leonard's relationship.

Sheldon and Wolowitz's fight over a parking spot at the university impacts the whole gang.

When Amy gets sick, Sheldon tries to nurse her back to health; Wolowitz and his father-in-law plan a fishing trip.

During a game, Sheldon revisits Christmas memories; Amy, Penny and Bernadette look for a date for Koothrappali.

When Sheldon is accused of sexual harassment, he ends up getting Raj, Leonard and Wolowitz in trouble.

As the guys don costumes and go on a road trip to a comic book convention, the ladies decide to stay home and try to interpret a comic book.

Sheldon faces a crisis of confidence when he is forced to work with his nemesis, Barry Kripke; Raj and Howard buy expensive action figures of themselves.

A fight between Sheldon and Leonard impacts Amy and Penny's living arrangements; while Howard is away, Raj helps Mrs. Wolowitz out.

The guys search for a perfect Valentine's Day gift for their significant others; Stuart and Raj host a "lonely people" party at the comic book store.

After a bad date, Koothrappali decides to never leave his apartment; Penny's acting skills impress Sheldon.

Leonard, Sheldon and Wolowitz talk to junior high girls about science-related careers; Raj plans a date with Lucy.

Howard considers whether or not he should open a letter from his father; Penny and Leonard host a "grown-up" cocktail party.

The girls get involved when Leonard, Sheldon and Raj compete for tenure at the University.

Amy tries to help Sheldon get over his compulsive need for closure when one of his favorite TV shows is canceled; Raj discovers a secret about Lucy.

Leonard and Sheldon hire the host (Bob Newhart) of their favorite childhood TV show to perform; Bernadette and Howard run into trouble while dog-sitting for Raj's pet.

Amy and Sheldon's relationship takes a surprising turn during a game of "Dungeons & Dragons"; Lucy and Koothrappali have an awkward date.

When Leonard receives an exciting opportunity to work overseas, Penny and Sheldon are thrown for a loop.

Sheldon and Wolowitz's fight over a parking spot at the university impacts the whole gang.

When Amy gets sick, Sheldon tries to nurse her back to health; Wolowitz and his father-in-law plan a fishing trip.

During a game, Sheldon revisits Christmas memories; Amy, Penny and Bernadette look for a date for Koothrappali.

When Sheldon is accused of sexual harassment, he ends up getting Raj, Leonard and Wolowitz in trouble.

As the guys don costumes and go on a road trip to a comic book convention, the ladies decide to stay home and try to interpret a comic book.

Sheldon faces a crisis of confidence when he is forced to work with his nemesis, Barry Kripke; Raj and Howard buy expensive action figures of themselves.

A fight between Sheldon and Leonard impacts Amy and Penny's living arrangements; while Howard is away, Raj helps Mrs. Wolowitz out.

The guys search for a perfect Valentine's Day gift for their significant others; Stuart and Raj host a "lonely people" party at the comic book store.

After a bad date, Koothrappali decides to never leave his apartment; Penny's acting skills impress Sheldon.

Leonard, Sheldon and Wolowitz talk to junior high girls about science-related careers; Raj plans a date with Lucy.