The Big Bang Theory (2007)

Sheldon and Amy are devastated after learning from a Russian paper that Super Asymmetry has already been discovered and disproven. Also, ultra-competitive Bernadette asks Stuart’s girlfriend, Denise, to teach her how to beat Howard in a popular videogame.

Sheldon and Amy are still down about their theory being disproven, but a VHS tape from Sheldon’s past inspires him not to give up. Also, Bernadette turns into a pageant mom when she tries to help Wolowitz ace his Magic Castle audition.

Penny and Leonard organize a paintball game that results in mayhem when Sheldon is jealous of Amy. Also, Koothrappali catches Anu with her ex-boyfriend, and Stuart doesn’t want to move in with Denise.

Penny's ex-boyfriend, Zack, and his wife want a baby, but when Zack is infertile, they ask Leonard for help. Also, Koothrappali attempts to mend things with his ex-fiancée, Anu.

Sheldon and Amy's super asymmetry theory is proven by two physicists, Dr. Pemberton and Dr. Campbell from Chicago, who then try to kick Amy off the Nobel nomination. Also, Bernadette has a big success at work and Penny's going to be a part of it—whether she wants to be or not.

Sheldon is thrilled to help Bernadette and Wolowitz navigate bureaucratic paperwork, until he discovers they are breaking the law. Also, Leonard is disappointed when his friends exclude him from a scientific project.

Penny tries to seduce an abstaining Leonard to ruin his "donation" for her ex-boyfriend, Zack, and his wife, Marissa. Also, Wolowitz, Bernadette, Anu and Koothrappali turn Koothrappali's canceled bachelor party into a couple’s trip aboard the "vomit comet."

The gang finds out Wil Wheaton hosts a celebrity Dungeons and Dragons game involving William Shatner, Joe Manganiello, Kareem Abdul-Jabbar and Kevin Smith. Deception and betrayal are the path to make it to the one open seat.

When Penny and Bernadette go to San Diego for a pharmaceutical sales convention, Wolowitz is in charge of the kids. Also, Sheldon finds a book on experimenting on kids, and the guys plus Amy make a day of it.

When competitors Pemberton and Campbell charm America on a publicity tour, Sheldon and Amy try to bring Nobel laureates Kip Thorne, George Smoot and Frances Arnold to their side. Also, Halley’s fear of the dark leads to opportunity and conflict for Howard, Bernadette and Stuart.

The concept of what it would mean for women everywhere if Amy were to win a Nobel Prize causes Amy to have a meltdown. Also, Koothrappali and Wolowitz try to relive the good old days after Wolowitz buys a scooter that looks like the one he had years ago.

Koothrappali is worried people won't take him seriously in his own field after publishing a paper that suggests he may have discovered alien life. Also, Leonard wants to be the principal investigator on a plasma physics study.

Kripke has proof that Dr. Pemberton plagiarized his thesis in college, and Sheldon and Amy aren't sure if they should turn him in or not. Also, Wolowitz is happily surprised to learn that Bernadette wasn't the only waitress at the Cheesecake Factory who had a crush on him back in the day.

Leonard is pleasantly surprised when Beverly comes to visit and she's genuinely kind to him, until he finds out the real reason she's there. Also, Denise and Stuart overstay their welcome at the Wolowitz house.

Sheldon and Amy await big news.

Bernadette and Wolowitz leave their kids for the first time; Penny and Leonard try to keep a secret; Sheldon and Amy stick together; and Koothrappali makes a new friend, as the gang travels together into an uncharted future.

Sheldon tries to teach the guys a lesson after they cut him out of a potentially valuable Bitcoin investment. Also, a seven-year-old video reveals a secret about Leonard and Penny's relationship.

Sheldon and Amy try to eliminate stress from wedding planning by applying math to the process. Koothrappali “breaks up” with Wolowitz after realizing his best friend is actually hurting his confidence.

Sheldon and Wolowitz plan birthday celebrations for Amy and Halley, respectively. Also, Leonard receives a Christmas letter from his brother that causes him to spiral out about his own lack of accomplishments.

To discover who would be most qualified to be best man and maid of honor at their wedding, Sheldon and Amy subject their friends to a series of secret experiments. Also, Penny reveals her true feelings about Amy.

When Sheldon kicks Amy out to work solo, she and Leonard bond during a series of science experiments. Also, Bert the geologist replaces Wolowitz in the band Footprints on the Moon, and Sheldon finds Penny a surprising source of scientific inspiration.

Koothrappali finds himself in the middle of domestic drama when he learns the woman he's dating, Nell, has a very upset husband, Oliver. Also, when Sheldon rents his old room back for a quiet place to work, he drives Leonard crazy by being a model tenant.

When Sheldon petitions Wil Wheaton to appear on the new Professor Proton show, Wil offers a role to Amy instead. Also, Penny gets angry when she thinks the female protagonist in Leonard's novel is based on her.

When Bernadette won't go into labor, all her friends try different tactics to get things started. Also, Wolowitz confronts Bernadette after Amy accidentally reveals she's already chosen their son's name.

Leonard jumps through hoops to help secure the perfect wedding venue for Sheldon and Amy. Also, Bernadette and Wolowitz have a hard time deciding who should stay at home with the kids and who should go back to work.

Penny gets the opportunity to host Bill Gates at work when his company wants to partner with her pharmaceutical company. Also, Leonard, Koothrappali and Wolowitz do everything in their power to meet him, while Sheldon thinks he is the victim of an April Fools prank.

When Leonard learns Sheldon is the president of the tenants association, he decides to run against him. Also, Bernadette encourages Wolowitz and Koothrappali to find the owner of a drone after they find it in the backyard.

A brilliant but reclusive scientist, Doctor Wolcott, invites Sheldon to his cabin in the middle of nowhere, and Leonard, Raj and Howard go along for the trip. Also, Penny and Bernadette improvise after Amy doesn’t like the tame bachelorette party they planned for her.

Sheldon’s comic book store experiences changes when writer Neil Gaiman puts Stuart’s store on the map. Also, Koothrappali takes credit for Penny’s astronomical discovery, and friendships are threatened.

Sheldon goes to Vegas to win money for science. Also, Penny and Bernadette take Amy wedding dress shopping, but her terrible choice entangles them in a web of lies.

When Sheldon learns that his mother won’t attend his wedding unless he invites his brother, Georgie, he and Leonard travel to Texas to end a family feud. Also, the Wolowitz kids inadvertently infects Amy, Bernadette, Wolowitz and Koothrappali with pinkeye.

When Amy’s parents and Sheldon’s family arrive for the wedding, everybody is focused on making sure all goes according to plan – everyone except the bride and groom.

When Bert, a Caltech geologist, wins the MacArthur Genius fellowship, Sheldon is overcome with jealousy. Also, Wolowitz finds an old remote control Stephen Hawking action figure he invented.

Sheldon and Leonard must divide up their possessions and remove Penny's things from 4B. Meanwhile, Koothrappali and Stuart fight to be the most helpful during Bernadette's final weeks of pregnancy.

Amy's desire to have an intimate night with Sheldon on her birthday is interrupted by Bernadette going into labor.

Sheldon and Amy visit Leonard and Penny for the first time since the holidays and share details about their terrible trip to Texas.

When Penny feels that Leonard is taking her for granted, she decides to go on a spa weekend with Amy. Also, Wolowitz and Koothrappali try to fix a squeaky floorboard in the baby's room.

Sheldon beta-tests an MIT invention after hearing it can help him read people's emotions. Also, Leonard can't hide his feelings when Penny announces her brother is coming to town, and Raj invites his ex-girlfriends over to give him dating advice.

Leonard and Wolowitz try to distract Sheldon when he slows the progress of their guidance system. Also, Penny and Amy take Bernadette out for the night, leaving Raj and Stuart to care for baby Halley.

Sheldon and Amy have their first fight since moving in together, and Koothrappali is shocked at the realities of financial independence when he stops receiving support from his father.

The guys' annual trip to Comic Con is in doubt when Raj can't afford to go and an unexpected replacement is considered.

Raj searches for a cheaper living arrangement and it creates unexpected conflict among everyone.

Leonard, Penny and Raj adjust to their new living arrangement and Sheldon takes an interest in Amy's work.

Sheldon pushes himself to the limit when he collaborates on projects with Leonard and Wolowitz as well as Amy on the same day. Also, Bernadette is nearing the end of her maternity leave and must return to work.

Howard and Bernadette have a hard time leaving Halley in day care when Bernadette returns to work. Also, Bert introduces the gang to his new girlfriend, Rebecca.

Leonard isn’t thrilled when Penny considers taking a new job offered by her ex-boyfriend, Zack.

After celebrating the completion of the top-secret Air Force project, Leonard, Sheldon and Howard get an unwelcome surprise; Amy receives an offer for a summer position at Princeton as a visiting researcher.

The gang is concerned when Sheldon’s former admirer, Dr. Ramona Nowitzki, resurfaces while Amy is away at Princeton.

It’s Thanksgiving. Sheldon and Amy go on a lunch date to the aquarium as friends. Meanwhile, Howard, Bernadette, Raj and Emily help out at a soup kitchen and Leonard and Penny make their first Thanksgiving dinner as a married couple.

Sheldon has a revelation when he realizes why a song was stuck in his head. Also, Amy invites Dave over for dinner despite their previously awkward date, and Wolowitz and Koothrappali become obsessed with a fan of their band, "Footprints on the Moon."

As the guys prepare to go to the premiere of the new Star Wars movie, Sheldon plans a special event for Amy's birthday.

Leonard visits a psychiatrist so Penny can make a sales call. Stuart moves out of the Wolowitz house. Sheldon works with Raj looking for extra-solar planets.

The gang decides to head to Vegas for the week on a party bus. Sheldon learns about the importance of empathy and saying sorry.

Sheldon is thrilled when his Meemaw comes to visit, but his excitement quickly fades when she butts heads with Amy. Also, Raj meets a new girl at the comic book store who makes him question his relationship with Emily.

Sheldon and Amy host a live Valentine's Day episode of Fun with Flags, Leonard and Penny grapple with getting older, Howard and Bernadette find a surprise in their hot tub and Raj is torn between Emily and the cute girl he met at the Comic Bookstore.

When the gang finds out about Bernadette's pregnancy, they celebrate by singing karaoke. Also, Bernadette is concerned when Wolowitz freaks out over her pregnancy announcement, and Wolowitz is convinced he must make more money to provide for a baby.

After more than nine years together, the gang finally celebrates Sheldon’s birthday, surprising him with a special guest.

Sheldon works up a contract to split their portion of their guidance system invention royalties, but Bernadette does not like how it's done. Raj must again decide between Emily and Claire when they both contact him.

Amy is shocked at a revelation from Sheldon after she buys him a new laptop. Koothrappali sells out Leonard and Wolowitz after they lie to their wives in order to attend an early screening of a movie.

Secrets are revealed when Amy and Sheldon join Penny and Leonard on a weekend cabin trip. Raj is more excited about Howard's and Bernadette's impending parenthood than they are.

Everyone must choose sides when a small argument between Leonard and Sheldon erupts into a heated fight during a group get-together.

Sheldon and Bernadette spend a night together while the rest of the gang goes to a wine tasting party, but things get uncomfortable for Raj when Zack also attends and takes an interest in Claire.

Sheldon hires Stuart to spend the day with Amy when he’d rather go to a movie screening. Also, Leonard’s mother, Beverly, comes to town and Penny struggles to make a connection with her.

Leonard and Penny get remarried in front of their friends, Leonard's parents, Beverly and Alfred and Sheldon's mother, Mary, who finds something in common with Alfred. Howard gets an unknown email from the Air Force about his invention.

When Leonard gets minor surgery on his nose, Sheldon is the one in need of sympathy. Meanwhile, Raj's parents' impending divorce causes Howard and Bernadette to work on their own marriage.

While Sheldon says a tearful goodbye to the final installment of "Fun with Flags," Leonard, Howard and Raj search for something significant in a dead professor's research and Bernadette is shocked to learn of her co-workers’ true feelings from Penny.

Leonard and Howard turn to Raj for help in dealing with a work emergency when they nearly come to blows after blaming each other for a potential disaster at the university. Amy throws an authentic Victorian Christmas party, while Sheldon seeks revenge on her for making him celebrate the holidays.

Wolowitz tries to distract Raj, who is anxiously awaiting data from a space probe he helped launch. Meanwhile, Sheldon and Leonard go dress shopping with Penny and Amy.

The gang tries to help Sheldon when he becomes stuck in a rut at work by increasing his anxiety level. Howard teases Raj with a new game called "Cinnamon or Emily?"

Leonard and Sheldon publish a paper which is widely accepted except for comments from an internet troll. Meanwhile, the girls reminisce about embarassing incidents from their past.

Wolowitz receives some shocking news as everyone prepares for the reopening of Stuart’s comic book store. Penny teaches Sheldon how to “let it go,” but can’t follow her own advice after she learns something infuriating about Amy. Also, Leonard and Raj think they've spotted Nathan Fillion at a restaurant.

As a joke, Sheldon and Penny try an experiment designed to make participants fall in love. Also, Leonard, Amy, Raj and Emily spend the evening trying to escape a room with a “zombie.” And, after returning from Mrs. Wolowitz’ funeral, Bernadette and Howard run into trouble at the airport.

Trouble arises when Amy learns Sheldon has applied for a one-way mission to colonize Mars. Also, a trip to the pet store ends in a fight for Sheldon and Amy, Leonard surprises Penny with a very “adult” purchase, and Raj is caught snooping in Emily’s apartment.

Friction ensues when a magazine fails to mention Leonard in an article about the paper he co-wrote with Sheldon. Also, a blackout at Mrs. Wolowitz’s home leads to a final family dinner in her honor.

When Leonard and Sheldon are invited to speak at UC Berkeley, they take a detour to try to meet an idol. Also, when Bernadette and Howard battle over the fate of his Doctor Who TARDIS, Raj and Amy offer to settle the dispute with a game of ping pong.

When Sheldon and Amy build a blanket fort, they come to major crossroads in their relationship. Also, Wolowitz meets the half-brother he never knew he had, and when Penny is invited to appear on Wil Wheaton’s podcast, she and Leonard have a huge, on-air argument.

When Raj is asked to create a message in case a NASA mission discovers alien life, the guys fight over what he should do. Also, Penny is torn between auditioning for a movie or keeping her successful pharmaceutical sales job.

Wolowitz questions his engineering abilities when he and Sheldon can’t get a toy drone to fly. Meanwhile, a cancelled flight nearly prevents Leonard from giving the commencement address at his former high school, and Raj pits his parents against each other when his father cuts him off financially.

Personalities collide when Sheldon and Leonard’s mothers finally meet. Meanwhile, Howard finally decides to “man up” and do his fair share of the housework – but not without a little help from his friends.

Sheldon pushes Leonard and Penny to choose a date for their wedding and deals with dramatic changes in his own relationship with Amy.

An upset Sheldon protests when the entire gang drags him to Mrs. Wolowitz's house for Thanksgiving. Meanwhile, Penny and Leonard must deal with a mistake from her past.

Sheldon faces a crisis after Leonard disproves his accidental scientific discovery. Meanwhile, Raj must stay with Howard & Bernadette for a week.

While Sheldon is in Texas, the rest of the gang realize how much he has changed their lives as they decorate the apartment for Christmas.

As Leonard tries to help Penny with a disappointment, Penny asks him a bold question about their relationship; Meanwhile Raj and Stuart practice their skills at talking to women and Sheldon wants to learn how to be funny.

Sheldon must learn how to relax when he is forced to take a vacation; Leonard tries to support Penny after she quits her job; Bernadette needs to replace one of Howard’s comic books.

Unable to get Comic-Con tickets, Sheldon tries to hold his own convention and ends up spending a wild evening with James Earl Jones; the ladies try to act maturely.

On Valentine's Day, Sheldon and Amy go on a trip to wine country with Howard and Bernadette; Penny and Leonard rush Raj's dog to the vet.

When Leonard buys a dining room table, Sheldon re-evaluates the changes in his life; Bernadette is torn when Wolowitz gets the chance to go back to space.

Bernadette tries to negotiate peace between Sheldon and Wolowitz; Penny receives an embarrassing offer; Raj wants Amy to write to a woman on his behalf.

Sheldon is faced with a new reality when he visits his mom in Houston after a trip to NASA; a murder mystery party starts arguments.

Raj struggles with guilt when he dates two women at once; Penny has a chance to play a part in a cheesy movie; Sheldon is torn between two gaming systems.

Sheldon has a personal crisis when he decides string theory is a waste of his time; a double date ends in embarrassment for Howard.

Sheldon gives spontaneity a try, which causes unexpected friction for Penny, Bernadette and Amy; Raj asks Howard for help with preparation for a date with Emily.

Professor Proton helps Sheldon deal with grief; Leonard gets into a competition with Penny; Bernadette and Amy prepare a "Star Wars Day" gift for the guys.

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. Also, Howard and Bernadette struggle to care for Mrs. Wolowitz when she is injured.

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 too.

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 when Sheldon cleans his closet; Penny and Leonard host a "grown-up" cocktail party.

The girls get involved when Leonard, Sheldon and Raj LL 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 of their favorite childhood TV show to perform for them; 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 is considered for an exciting research opportunity, Sheldon becomes jealous and tries to scare him into backing out. Meanwhile, Raj's relationship with Lucy is strained when he tries to get her to meet his friends.

Leonard and Penny try hanging out as friends on a 'non-date,' but end up purposely ruining each others chances with perspective dates. Meanwhile, Sheldon enlists the help of Bernadette and Amy to overcome his fear of birds.

Sheldon considers taking his relationship with Amy to the next level when Stuart from the comic book store asks her out on a date.

When Leonard's former high school tormentor resurfaces, Leonard must confront him. Meanwhile, Penny realizes she did her fair share of tormenting in the past.

Sheldon gets in trouble with Amy when he isn't impressed by her recent accomplishment, and Howard must come to grips with Bernadette's dislike of children.

Leonard, who broke up with Priya, asks Penny out to a spur-of the-moment romantic dinner for two, and the duo contemplates resuming their relationship.

Leonard and Penny deal with the idea of starting a relationship again and Raj finally finds a "woman" he can talk to without being drunk. Meanwhile, Sheldon decides to start a YouTube series entitled "Sheldon Cooper presents Fun with Flags" with the help of Amy.

Sheldon's selfish demands force Leonard to reconsider their friendship. Meanwhile, Wolowitz tries to pick his astronaut nickname.

When Sheldon is forced to take his vacation, he goes to work with Amy in her neurobiology lab. Also, Bernadette wants Howard to sign a pre-nup.

Sheldon and his rival Barry Kripke fight it out over the availability of a new office. Penny gets a gift from Amy that really tests their friendship and it doesn't end well.

Sheldon becomes agitated when his regular barber is out sick. Astronaut training causes Howard to reconsider wanting to go into space. Penny beats Leonard in chess, the first time she plays.

Sheldon must choose between joining Amy at her aunt's birthday party or playing videogames all weekend with the guys.

Penny buys Leonard and Sheldon “Star Trek” collectibles as a thank-you, leading Sheldon to be haunted by Mr. Spock. Meanwhile, Raj decides he has met the “Future Mrs. Koothrappali” after his parents set him up on a date.

When Wolowitz gets to work with Stephen Hawking, Sheldon is willing to do anything to meet his hero.

After the guys throw Howard a bachelor party, Bernadette reconsiders marrying him after learning about his sexual history.

When NASA moves up Howard's mission, he must face his fears and Bernadette's dad, thus putting the wedding plans in jeopardy. Meanwhile, Leonard says something surprising to Penny in the bedroom.

As Howard's mission to space approaches, Howard and Bernadette decide to get married before his launch, causing the gang to scurry into overdrive in an effort to stage the wedding.

Penny asks Leonard to lie to her father, while Howard, Raj and Bernadette pull an all-nighter at a telescope.

Amy finds she has sexual feelings for Penny's ex, while Koothrappali and Wolowitz try to prove who would be the better superhero.

The guys find a "super" use for Penny's new boyfriend, Zack, when they enter a costume contest as the Justice League.

Leonard's idea for a smartphone app derails his friendship with Sheldon.

When the gang road trips to a conference, tensions run high when Bernadette runs into her ex-boyfriend.

Hoping it will make him a better teacher, Sheldon has Penny give him acting lessons. Raj has fantasies about a friend's girlfriend.

A wealthy donor to the university makes Leonard consider how far he's willing to go for the sake of science.

As Wolowitz contemplates taking things with Bernadette to the next level, Leonard rekindles his relationship with Raj's sister Priya.

Sheldon becomes concerned when everybody begins to hang out at Raj's apartment and discovers Leonard is the center of the group.

Sheldon is baffled by Wolowitz's magic trick. Meanwhile, Leonard realizes dating Priya may make it impossible to continue being friends with Penny.

The guys go all out to help Sheldon find the person responsible for hacking his online gaming account, while the girls' hatred for Priya increases.

Sheldon and Amy decide to start several rumors about the others as a test. Meanwhile, Howard takes his relationship with Bernadette to an even higher level.

When Priya finds a loophole in the roommate agreement to throw Sheldon out for the night, Penny, Amy and Bernadette take him to a nightclub.

Raj attempts to cure his social anxiety disorder while Penny uses Bernadette to spy on Leonard and his girlfriend.

When Howard finally breaks the news to his mom that he's engaged to Bernadette, it lands her in the hospital.

When Bernadette receives her PhD, Wolowitz feels emasculated. Raj and Leonard swap apartments and Penny does something she regrets.

After he's humiliated on National Public Radio, Sheldon vows to destroy Kripke, while Wolowitz tries not to destroy his new relationship with Bernadette.

Penny gets help from Sheldon in order to understand what Leonard's work is, while Wolowitz develops a jealousy when Leonard starts hanging out with his new girlfriend.

A Christmas visit from his mother has Leonard discovering she's kept a lot of news from him that she shares with Sheldon and worrying if she'll approve of his romance with Penny.

Leonard is aghast to find out a secret of Penny's: she believes in psychics. Meanwhile, Sheldon tries to assist Koothrappali in picking up a girl at a university mixer.

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

Sheldon's search for the answer to a physics problem leads him to work at the Cheesecake Factory with Penny.

Leonard can only bring one guest on a trip to see CERN's Large Hadron Collider (the world's largest and highest energy particle accelerator) in Switzerland on Valentine's Day.

Sheldon winds up in traffic court when he gets a ticket because of Penny.

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

Sheldon's friends come to his aid when his fear of public speaking stands between him and a coveted award.

A fight between Leonard and Penny threatens their relationship, while Sheldon battles Wil Wheaton in bowling.

When Leonard and Penny aren't speaking, Sheldon goes to extremes to keep them both happy.

Leonard and Sheldon compete for the attention of a famous female physicist.

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

While Penny worries that dating Leonard has ruined her for normal guys, Wolowitz and Koothrappali search for Sheldon's perfect match online.

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.

Penny's criticism of Wolowitz's romantic life pushes him into depression and AWOL for a fighting robot battle the rest of guys are depending on him for.

Sheldon creates a scientific procedure for making friends.

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.

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 is on board the train they are taking to San Francisco.

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

Penny squares off with a new beautiful female neighbor who may become the building's "new Penny."

When a fellow comic book enthusiast hits on Penny it leads to Leonard and Howard going to a bar's on Ladies' Night.

Leonard and Koothrappali escort a heartbroken Wolowitz to Las Vegas, and Sheldon becomes locked out of his apartment and must stay with Penny.

Penny's second date with Stuart sees her making a comment that gives Leonard new hope for a relationship with her. Wolowitz realizes there's a crucial error in a NASA project he's working on.

The guys' plan to work over the summer at the North Pole makes Penny revaluate her feelings for Leonard.

When they're invited to present at a physics conference, Sheldon's reluctance to share the credit leads to a tiff between him and Leonard, and Penny's intervention only exacerbates the situation.

Leonard and Sheldon each lie to avoid seeing Penny's concert, but Sheldon's lie is a bit too complicated for his own good.

With his friends knowing how sour he acts when sick—and avoiding him as a result—Sheldon is nursed by Penny, who hasn't a clue what she's in for.

When Sheldon meets a 15-year-old physicist prodigy, he's rattled and threatened and Leonard tries to help him look for ways to debunk his research.

Sheldon finds himself booted from the gang's Physics Bowl team and replaced by Leslie Winkle, so he forms his own team, hoping to prove he's superior.

When the guys buy a time machine prop from a classic 1960 movie, Penny lashes out at Leonard and he decides it's time to give up his habit, much to his friends' protestation.

The rest of the gang fall for Sheldon's twin sister, and Leonard's plan to win her heart is derailed when Sheldon declares he'll be the one to decide who can date her.

Penny wants to throw a surprise party for Leonard, but Sheldon's indulgence at an electronics store throws her off-track. Meanwhile, Howard makes a terrible sacrifice for the sake of the surprise.

Penny's break-up spurs Leonard to summon up the courage to ask her out, and each head to Sheldon for advice on their upcoming date.