The Big Bang Theory

When Penny divulges a secret to Sheldon, he fears he won't be able to keep it from Leonard and decides to move out.

Leonard is caught in the middle when he resumes a relationship with Leslie Winkle, a fellow physicist who's Sheldon's archenemy.

When Penny gets locked out of her apartment, Sheldon invites her in and introduces her to an online video game that quickly takes over her life.

When a magazine write-up goes to Raj's head, he's forced to apologize to Penny, who gets the brunt of his obnoxious behavior.

When Leonard's new schedule makes it impossible for him to drive Sheldon to work, the gang holds an intervention to force Sheldon to get his license.

Sheldon becomes distressed when an admiring grad student forces his way into his life and declares herself his assistant.

Penny's faux pas sets off an escalating feud with Sheldon that Leonard decides to end by calling in the ultimate weapon: Sheldon's mother.

Howard loses a potential girlfriend to Leonard, and Sheldon expands the classic game of rock-paper-scissors to include Mr. Spock and a lizard.

Believing that Dr. Stephanie Barnett is Leonard's ideal mate, Sheldon goes overboard to prove to her how great Leonard is.

Penny is the only one who seems to understand that Leonard's new girlfriend has moved into his and Sheldon's apartment.

Sheldon becomes obsessed with finding the perfect Christmas gift for Penny, and Leonard is crushed when a cool fellow scientist starts dating Penny.

The guys plan to enter a robot fighting championship, but things take a disastrous turn when Sheldon learns that Barry Kripke has his own robot.

When he hears that rival scientist Barry Kripke has access to a new computer, Sheldon goes to great lengths to try to become his friend.

When they learn of Penny's financial problems, Sheldon lends her money and Leonard attempts to get Penny's ex-boyfriend to repay an old loan.

Leonard's distress over a visit from his mother, a judgmental psychiatrist, only grows when his friends bond with her as he never has.

Howard strikes up a romance with Leonard's ex-girlfriend Leslie Winkle, and Penny accidentally hits Sheldon's spot on the couch with a paintball gun.

The guys geek out when they learn that they're aboard the same San Francisco-bound train as Summer Glau of "Terminator: The Sarah Connor Chronicles."

The guys pitch in to help make and sell Penny's handmade floral barrettes, but they can't keep up when the product proves successful.

The guys grow infatuated with a sexy new neighbor, who has no problem using them to get what she wants. But Penny sees right through her.

Comic book shop owner Stuart asks Penny out on a date, prompting a jealous Leonard to visit a bar with Howard and Raj in search of romance.

When Leslie breaks up with Howard, Raj and Leonard cheer him up with a trip to Las Vegas. Meanwhile, Sheldon spends the night at Penny's apartment.

Howard's celebration for the debut of his International Space Station toilet is short-lived when he realizes that it will explode after ten flushes.

Sheldon gets a grant to spend three months at the North Pole and asks the guys to go with him, but Leonard hesitates at being away from Penny so long.

Back from the North Pole, the guys reveal that they doctored Sheldon's experiment results as a prank, causing him to flee home to Galveston in anger.

When their first romantic evenings go awry, Penny and Leonard agree to return to just being friends, even though it's not what either one wants.

Sheldon deals with Penny's frequent visits to Leonard's room by conditioning her with chocolate; Raj and Howard enjoy a goth-themed night out.

Raj must get a new job or face deportation when his research ends, so Sheldon hires him as an assistant, a situation that soon goes to Sheldon's head.

Penny sets Howard up with one of her friends, and Sheldon enters a collectible card game tournament to get revenge on guest player Wil Wheaton.

Leonard tries to fit in when Penny throws a party to watch a football game, and Raj develops abandonment issues with Howard.

Leonard and Penny's bickering drives Sheldon to stay with Raj and then Howard, but their fights with their parents are just as disturbing.

Sheldon helps Penny when she slips in the shower. Raj, Leonard and Howard's meteor shower viewing party gets a boost from some "magic" cookies.

Bernadette asks Howard where their relationship is headed, and Barry Kripke pulls a prank on Sheldon during an NPR interview.

Bernadette's interest in physics draws her to Leonard, sending a jealous Penny to Sheldon for a crash course on the subject.

When Leonard's mother visits at Christmas, he finds out that his parents are getting divorced -- which Sheldon has known about for weeks.

Leonard makes fun of Penny for consulting a psychic, then makes it up to her by visiting one himself. Raj bribes Sheldon to act as his wingman.

When his apartment is burglarized, Sheldon begins to feel unsafe in Pasadena and researches new places to live.

Sheldon hopes that a menial job will clear his mind enough to solve a tough problem. Meanwhile, the rest of the gang enjoys roller disco night.

When Leonard is invited to visit Switzerland's Large Hadron Collider, his decision to bring Penny along leaves Sheldon feeling betrayed.

Sheldon learns that he must be in court to fight a traffic ticket the same day that Stan Lee is due to appear at the comic book store.

The guys find life imitating art when the "Lord of the Rings" ring they bought at a garage sale turns out to be the one actually used in the films.

Nervous about a speech, Sheldon gets advice and help from Penny, Leonard and Raj ... then gives the speech drunk on the big night.

Leonard is stunned when Penny responds "thank you" to his "I love you," and Sheldon sees a chance to get back at Wil Wheaton while bowling.

When Penny and Leonard break up, Sheldon continues his friendship with Penny, which Raj and Howard tell him just isn't done when a buddy gets dumped.

A physicist visiting from Princeton creates waves when she has a one-night stand with Leonard, then takes up with Raj and Howard.

A feud between Leonard and Sheldon prompts Penny to ask why the two live together in the first place, and Leonard tells her in a series of flashbacks.

The guys' lunar experiment party turns ugly, thanks to Penny's date. Meanwhile, an online dating site matches Sheldon with Amy Farrah Fowler.

Howard is attacked by a robotic arm he borrowed from the Jet Propulsion Laboratory, and Penny chaperones Sheldon's first date with Amy Farrah Fowler.

A freak accident causes Sheldon to interact with others remotely via the Mobile Virtual Presence Device (MVPD), which Penny fittingly dubs "Shel-Bot."

Sheldon and Amy grow closer every day, until a minor disagreement causes them to split and Sheldon to seek solace by adopting 25 cats.

A chance meeting gives Howard a second chance with Bernadette, and Raj battles Sheldon over the addition of a desk in their office.

Sheldon avoids Amy when she wants to introduce him to her mother, and Howard and Bernadette set Leonard up with an obnoxious blind date.

Leonard's secret tryst with Raj's sister Priya prompts the guys to admit years' worth of secrets they've kept from one another.

Interviewed for Howard's security clearance, Sheldon blabs about the Mars Rover crash, Raj is nearly deported, and Leonard hits on the interviewer.

Sheldon steals a print of "Raiders of the Lost Ark" from a theater, and Amy proves socially inept during a girls' night with Penny and Bernadette.

When her father visits, Penny asks Leonard to pretend that they're still together, since he's the only one of her boyfriends her dad has ever liked.

When Amy is attracted to Penny's ex, she describes these new feelings to a jealous Sheldon, who argues that she must be hosting an alien parasite.

The guys dress as the Justice League for a New Year's Eve party at Stuart's comic book shop, but Penny ditches to join her ex at a different event.

Leonard and Sheldon nearly come to blows over the development of a mathematics smartphone app, which has turned Sheldon into a megalomaniac.

Sharing cars and hotel rooms causes multiple issues when the entire group heads to Big Sur for a science conference.

Sheldon asks Penny for acting lessons to help him become more at ease at his new teaching job, and Raj fantasizes about Bernadette.

Leonard is honored when wealthy, elderly benefactor Mrs. Latham invites him for dinner, until he learns that he must sleep with her for a donation.

Angered by his dependence on his mother, Bernadette insists that Howard move in with her; Leonard is thrilled that Priya has come to visit.

When Amy calls Leonard the nucleus of their social group, Sheldon forms a new group, including his rival Barry Kripke, Penny's ex and LeVar Burton.

Priya pushes Leonard to end his friendship with Penny, and Sheldon becomes obsessed with figuring out Howard's card trick.

The guys take a road trip to confront the hacker who pillaged Sheldon's World of Warcraft account, and the girls confront Priya about her attitude.

Penny's rumor that Bernadette and Howard are breaking up leads the friends to panic and Amy to conduct an experiment in gossip.

Leonard's intensifying relationship with Priya violates multiple clauses in his roommate agreement with Sheldon, who's forced to rebuild the document.

When Priya invites Howard and Bernadette on a double date with her and Leonard, Penny uses the opportunity to get back at her.

Bernadette takes it personally when Howard's mother collapses upon hearing of their engagement, and Priya and Penny compare notes on Leonard.

Bernadette buys Howard a Rolex to celebrate her PhD and new job, and Raj becomes Sheldon's temporary roommate.

Raj is on everyone's lips when he sleeps with Penny and admits to fantasizing about Bernadette; Sheldon leads the department paintball team.

Sheldon's germ phobia goes into overdrive when Penny announces that the new chair he loves was salvaged from the side of the road.

Sheldon grows jealous when Amy takes Leonard as her date to a wedding. Meanwhile, Bernadette clashes with Howard about his mother.

Penny sets up Raj with her friend Emily, and the two hit it off. But Emily's motives soon become apparent to everyone but him.

Howard is thrilled to be going into space, but Bernadette fears for his safety. Meanwhile, Sheldon and Leonard are invited to a party by Wil Wheaton.

Sheldon's mother is in town for a few days as she waits for her cruise to set sail, but ends up spending her time with everyone but him.

Leonard is tempted to cheat on Priya with Alice, a girl he met at the comic book store. Meanwhile, Sheldon seeks revenge for a Halloween prank.

Amy is devastated when Bernadette and Penny don't invite her to go shopping for bridesmaids dresses, but Sheldon doesn't know how to comfort her.

A fight erupts when Penny and Leonard go to the movies as friends; Sheldon tries to rid the apartment of a bird that has him terrified.

Stuart asks Amy out, prompting a jealous Sheldon to ask Penny for a date out of spite. She refuses, but gives him advice on how to make Amy happy.

Leonard is contacted by a guy who bullied him in high school and hasn't changed. The incident prompts Penny to admit she was once a bully herself.

Sheldon buys Amy something pretty to make up for insulting her recent publication, and Bernadette reveals to Howard that she doesn't want children.

Leonard and Penny reconcile, but agree that they should progress slowly and keep their relationship secret, which has its drawbacks.

Penny and Leonard try starting their relationship again, Raj falls in love with Siri, and Sheldon and Amy launch the "Fun with Flags" webcast.

When Sheldon gets on Leonard's bad side, it doesn't take long to discover how much he relies on him in virtually every aspect of his life.

Sheldon spends his mandatory vacation "helping" Amy at her lab, and Bernadette's father wants Howard to sign a prenuptial agreement.

Sheldon and Barry Kripke play basketball to see who gets a vacant office, and Amy gives Penny an enormous, unflattering portrait of the two of them.

When his regular barber falls ill, Sheldon refuses to let anyone else cut his hair, and his lifestyle starts to change to reflect his longer locks.

The guys' plans for a weekend-long gaming marathon is derailed by Amy's aunt's 93rd birthday party, Bernadette's presence and other girlfriend issues.

Sheldon has a crisis of conscience when he swaps his broken vintage Star Trek transporter for Leonard's identical -- and unbroken -- specimen.

When he's asked to maintain Stephen Hawking's wheelchair during a guest lecture series, Howard realizes he has Sheldon in the palm of his hand.

Raj's drunken toast at Howard's bachelor party goes viral (thanks to Wil Wheaton), sending Bernadette on the warpath.

Howard's wedding plans are shaken up when NASA changes his launch schedule. Meanwhile, Leonard and Penny take their relationship to the next level.

While waiting for the countdown for his voyage into space, Howard reflects on the previous days, including his impromptu wedding to Bernadette.

Poor Raj is a third wheel on two different dates before he finally finds company. Wolowitz is nagged by his mother even though he's in outer space.

Penny is uncertain about her feelings for Leonard, which upsets Sheldon. Stuart is allowed to join the gang if he follows Sheldon's strict conditions.

While Wolowitz wrestles with cabin fever, Sheldon provokes a chain reaction of jealousy by hiring an attractive assistant to sort his old papers.

Wolowitz is distressed by the lukewarm reception he receives when he returns home from space, while Sheldon gets ultra-competitive during game night.

Raj and Stuart throw a Halloween bash, but it seems like the only one in a party mood is Penny, who gets turned on every time Leonard talks science.

Sheldon gets competitive while playing a word game with Stephen Hawking, and Penny is infuriated by Leonard's attempt to help her with her homework.

Wil Wheaton comes between Sheldon and Amy. Bernadette has second thoughts about forcing Howard to finally move out of his mother's house.

Raj and Howard go to extreme lengths to uncover Sheldon's secret afternoon activity, and Penny reveals how she really feels about Leonard.

Even though Sheldon doesn't drive, he's infuriated when Howard gets his parking spot at work, and their feud makes the whole gang miserable.

Howard finds surprising common ground with his father-in-law, while Amy relishes receiving some TLC from Sheldon when she's sick with the flu.

Sheldon reveals the reason for his deep-seated dislike of Santa Claus and Christmas, while Raj bonds with Amy over drinks during a girls' night out.

Sheldon gets all the guys in trouble with Human Resources when he uses inappropriate language to talk to Alex about hitting on a clueless Leonard.

The guys run into bad luck on a road trip to the Bakersfield Comic-Con. Back home, the girls discover that comic books aren't so bad.

Sheldon makes a shocking admission after a clash with Kripke jolts his self-confidence. Bernadette is furious when Howard spends too much money.

After a fight with Sheldon, Leonard decides to move in with Penny, causing a chain reaction of unhappy roommates moving from apartment to apartment.

Valentine's Day, a holiday loathed by all, arrives and prompts the various couples in the gang to celebrate in ways both typical and surprising.

Raj and Lucy have a hard time connecting; Sheldon and the gang are floored by Penny's performance in "A Streetcar Named Desire."

Sheldon, Howard and Leonard have trouble inspiring tween girls to take an interest in science, while Raj and Lucy find the perfect way to communicate.

The gang does its best to cheer up an anxious Howard after Sheldon unearths an unopened letter that Howard's father sent him on his 18th birthday.

The competition gets fierce when a tenured position opens up at the university, and it turns out that Ms. Davis from HR is on the deciding committee.

Amy tries to help Sheldon overcome his compulsive need for closure, while Raj reacts badly to revelations in Lucy's blog about his feminine side.

Sheldon and Leonard are thrilled to meet their childhood hero, TV scientist Professor Proton, but their anticipated party does not go as planned.

A weekend of "Dungeons and Dragons" goes awry when Raj leaves for a date with Lucy and Amy gets anxious about Sheldon's reluctance to become intimate.

The gang has mixed reactions when Leonard gets a work opportunity that will require him to be away for the summer, and Raj makes a major breakthrough.

Sheldon tries to comfort Penny, who's worried Leonard is having too good a time on the North Sea, while Raj gets on the wrong side of the head of HR.

When Sheldon learns that Leonard came home early to be with Penny, his feelings are hurt. Howard can't understand why he's feeling fat and vulnerable.

When the gang competes in a cutthroat scavenger hunt designed by Raj, it brings out the best -- and worst -- in everyone.

After Amy ruins one of Sheldon's favorite movies, he seeks revenge. Meanwhile, Leonard discovers a way to get Penny to do his bidding.

Sheldon must decide how much "Amy time" is too much after she takes a job at his university, putting their relationship to the test.

Sheldon's latest scientific breakthrough makes him feel like a fraud, and Howard's romantic gesture prompts Penny to step up her game with Leonard.

After Prof. Proton slights Sheldon, he seeks revenge by befriending rival TV host Bill Nye, the science guy. Meanwhile, Howard crashes a girls' night.

Leonard fails to keep Sheldon from overreacting when a past mistake comes to light. As penance, Leonard has to "walk a mile in Sheldon's shoes."

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

Leonard and Amy help Sheldon cope with the shame he's feeling after his accidental contribution to science is disproved.

While Sheldon is away, everyone gathers to decorate the Christmas tree and imagines what their lives would be like had they never met him.

When Penny's big acting break on "NCIS" is a bust, Leonard struggles to help her, which prompts Penny to ask him a bold relationship question.

When Sheldon is forced to take a vacation, he tries to relax but instead spends a lot of time with Penny after she quits her job.

When the guys can't get Comic-Con tickets, Sheldon decides to hold his own convention and ends up spending a wild night with James Earl Jones.

Amy persuades Sheldon to join her -- along with Howard and Bernadette -- for a romantic weekend in Napa Valley to celebrate Valentine's Day.

When Leonard buys a table, it causes Sheldon to reevaluate the changes in his life. Meanwhile, Wolowitz is offered a chance to go back into space.

Bernadette tries to make peace between Howard and Sheldon by having them travel together to Houston in an attempt to mend their friendship.

When Sheldon visits his mom, he's forced to confront a new reality. Meanwhile, Raj's murder-mystery party starts some fights within the gang.

While Raj is wracked with guilt over dating two women at the same time, Penny wrestles with whether to take a role in a cheesy movie.

Sheldon faces a personal crisis after deciding he's wasting his time with string theory. Meanwhile, a double date ends in embarrassment.

Leonard tries to help Sheldon free his mind by reinstating "Anything Can Happen Thursday," and Raj seeks Howard's help to prepare for a date.

Prof. Proton helps Sheldon cope with grief, while Leonard turns a relationship milestone into a competition with Penny.

A horrible day at work prompts Penny to reevaluate her life choices. Meanwhile, Howard and Bernadette struggle to care for bedridden Mrs. Wolowitz.

With his entire world changing around him, Sheldon is forced to confront an uncertain future. Meanwhile, Raj and Emily take things to the next level.

Sheldon is ready to come home after an incident on the train, so Amy and Leonard pick him up in Arizona. Penny interviews at Bernadette's company.

Sheldon becomes a junior professor, but he's required to teach a class. Amy enjoys being in the middle when Penny and Bernadette have a disagreement.

NASA asks Howard to throw out the first pitch at an Angels game. Sheldon and Amy outscore Leonard and Penny on a compatibility test.

Raj's girlfriend, Emily, finally meets Penny. Meanwhile, the guys consider investing in Stuart's comic book store.

The girls head to Vegas for the weekend, but Penny spends her time working instead of having fun. Back at home, the guys try to invent a hoverboard.

Sheldon and Raj test whether they could survive a dark-matter research expedition in a salt mine. Leonard and Penny bicker about money.

A doctor mistakes Penny's flirty sales pitch for attraction, while Amy and Bernadette debate whether female scientists should use their sex appeal.

Sheldon panics when the girls decide to recreate prom night on the roof of his building, thinking Amy will be expecting him to make a move.

A distraught Sheldon tries to talk Leonard out of getting minor surgery. Meanwhile, Raj's parents announce that they're getting divorced.

A professor's death prompts Leonard, Howard and Raj to reflect on their own work. Bernadette finds out how her co-workers really feel about her.

Raj swoops in to help Leonard and Howard deal with a work emergency. Amy throws an authentic Victorian Christmas party, irritating Sheldon.

Leonard and Sheldon learn a lesson about compromise when Penny and Amy take them shopping for dresses. Howard tries to distract a nervous Raj.

Sheldon enlists his friends to annoy him, hoping it'll put him in the right state of mind to make a breakthrough in his dark matter research.

Sheldon and Leonard deal with a rude commenter after they publish a physics paper online. The girls take an embarrassing trip down memory lane.

Stuart reopens the comic book store, Penny tries to help Sheldon stop dwelling on things and Howard receives some shocking news.

Sheldon and Penny try out an experiment that supposedly makes people fall in love. The rest of the gang spends the evening at an escape room.

Amy is upset when Sheldon applies to be part of a one-way mission to colonize Mars. Leonard has a risqué surprise for Penny.

A magazine fails to give Leonard credit for the paper he co-wrote with Sheldon, and they bicker during a dinner at Mrs. Wolowitz's house.

Invited to speak in Berkeley, Leonard and Sheldon take a side trip to George Lucas's ranch. At home, Howard and Bernadette argue about "Doctor Who."

Sheldon and Amy make a breakthrough in their relationship while building a blanket fort together. Penny appears on Wil Wheaton's podcast.

Sheldon and Howard try to take over a project that Raj is working on for NASA. Penny thinks about giving acting another try.

Leonard is scheduled to give a commencement speech at his old high school, but his flight gets canceled. Raj can't get his toy helicopter to work.

Sheldon and Leonard's mothers butt heads when they finally meet. Bernadette demands that Howard do his fair share of the housework.

After Sheldon hurts Amy's feelings on the anniversary of their first date, she decides it's time to reexamine their relationship.

Leonard's confession to Penny on their big day in Las Vegas creates a rift between them, while Sheldon and Amy also hit a bump in their relationship.

Leonard meets up with Mandy as he and Penny each face fears about their relationship. Sheldon shoots an angry episode of "Fun with Flags."

Raj and Howard plan a bachelor party for Leonard, but just getting there will be an adventure. The girls have a bachelorette party at Penny's place.

After learning that Leonard and Penny will move in together, Sheldon tries to emotionally travel in time to 2003, before he knew Leonard, Penny and Amy.

The guys take up fencing in an effort to get more exercise. Stuart tries to figure out how to get more girls to come to his store.

Sheldon and Leonard need to find liquid helium quickly when Swedish scientists set out to prove their hypothesis. Amy tries a dating app.

Sheldon gets emotional during an interview with Wil Wheaton for a "Star Trek" documentary. Bernadette wants to start renovating Howard's mom's house.

Penny, Bernadette and Leonard spy on Amy's date. Howard and Raj help Sheldon place an online ad to find a new girlfriend.

Amy and Sheldon go to the aquarium together as friends. Howard reluctantly agrees to volunteer at a soup kitchen. Penny and Leonard host Thanksgiving.

Sheldon gets a song stuck in his head but can't figure out what it is. Howard and Raj go overboard when they learn that their band has a fan.

Sheldon has to decide between spending time with Amy on her birthday and attending opening night of "Star Wars: The Force Awakens" with the guys.

Penny uses Leonard to make a sales pitch to a psychiatrist. Sheldon and Raj discover an asteroid. Stuart moves out of Howard and Bernadette's house.

After being annoyed by sick Sheldon, everyone goes to Las Vegas to get away from him. Sheldon learns the value of empathy and apologizing.

Meemaw comes to visit, but things don't go well when she meets Amy. Raj meets a girl he likes, prompting him to ponder his relationship with Emily.

Sheldon and Amy host a Valentine's Day episode of "Fun with Flags." Howard and Bernadette stumble on a new pet. Leonard and Penny start to feel old.

Howard freaks out when he hears big news, so the boys take him to a karaoke bar to calm him down. There, they come up with a new moneymaking idea.

Sheldon is reluctant to celebrate his birthday due to a bad childhood experience, but gives in when Amy and the others plan a big party for him.

The guys attempt to patent their idea but learn that the financial details will be sticky. Raj asks the girls for advice about Emily.

Amy buys Sheldon a new laptop, then learns something unusual about him. Howard and Leonard lie to their wives to see a screening of "Suicide Squad."

Amy, Penny, Leonard and Sheldon exchange secrets on a weekend trip to a cabin in the woods. Raj gets too involved in Bernadette's personal life.

A trivial disagreement between Leonard and Sheldon before a "Game of Thrones" viewing party devolves into a huge argument involving everyone.

Sheldon stays behind with Bernadette while everyone else goes to a wine tasting party. Raj gets into some hot water when he brings Claire along.

Leonard has Penny pick up his mother from the airport, and the two women struggle to make a connection. Sheldon hires Stuart to spend time with Amy.

Leonard and Penny plan a second wedding for friends and family, but it creates parental strife. Howard thinks the government is after Raj and him.

It's an uncomfortable wedding day for Penny and Leonard when it appears that his dad and Sheldon's mom may have hooked up and Penny's family arrives.

Air Force Col. Williams comes to see Howard about the quantum gyroscope. Bernadette is furious that someone at work has blabbed about her condition.

Bernadette confides in Raj she's not sure about being a mom. When Penny goes with Amy to Bert's party she's shocked to hear about Amy's reputation.

When Amy must leave her flooded apartment for weeks the logical thing to do is move in with Sheldon. Only Raj knows the sex of the Wolowitz baby.

Penny and Sheldon bond to complain about Amy and Leonard. While Howard and Bernadette plan a babymoon, Raj and Stuart take over their hot tub.

Penny is asked to sign autographs at a local fan convention, but it's Leonard who's the big hit. Sheldon and Amy host their first party together.

Sheldon and Amy return in "Fun with Flags." Amy's been lying to Sheldon about her apartment, and when he finds out, he has a big decision to make.

While working on a bioengineering project with Amy, Sheldon decides he wants them to have a baby. Raj is attracted to the office cleaning lady.

Sheldon has a hard time getting past his jealousy when Bert wins a huge grant. Howard's remote control Stephen Hawking raises questions, and eyebrows.

Leonard and Sheldon go to war over dividing up their stuff. Raj and Stuart are in a frenzy trying to be the most helpful to Howard and Bernadette.

Amy's annual birthday ritual is interrupted when Bernadette goes into labor. The gang reflects on how much their lives have changed -- except for Raj.

After the holidays Sheldon and Amy recall their trip to Texas to see his mother, and Leonard and Penny relive their argument over a Christmas tree.

Leonard and Penny turn to Sheldon and Amy for relationship advice. Raj and Howard need math and science to fix a squeaky floor in the baby's room.

Sheldon attempts to gain empathy and insight from an emotions reader. Raj gathers all his old girlfriends for a focus group to see what went wrong.

Leonard gives Sheldon a train experience holiday to get him out of the way so he and Howard can finish the project, then discover they need him back.

Amy feels Sheldon doesn't understand relationships when he blabs intimate information. The gang thinks Raj is too financially dependent on his father.

Raj's financial problems have him scrambling for money to go to Comic-Con, while Leonard and Penny outdo each other dreaming up couple’s costumes.

When Raj needs to move into a cheaper place, the gang offers help, then Beverly puts her own analytical spin on everyone's relationship issues.

Penny and Raj get along great when he moves in, leaving Leonard feeling like a third wheel. Sheldon and Amy's professional and personal lives collide.

After working on two projects at once, Sheldon finally crashes and can't remember the night before. Bernadette gets emotional about returning to work.

Bert has a hot new girlfriend. Could it have anything to do with his windfall? Howard, Bernadette and Stuart are anxious when Halley goes to daycare.

Leonard's nervous when Penny gets a good job offer from her old boyfriend Zack. Sheldon pouts that he hasn't reached his full potential soon enough.

The guys are restless after Col. Williams takes over their project. Amy gets a research opportunity requiring her to stay at Princeton for months.

Ramona Nowitzki returns and resumes her obsessive interest in Sheldon while Amy is away. He's the only one who doesn't see it, until he finally does.

Amy begins to have second thoughts about her response to Sheldon's proposal. Howard and Bernadette freak out over some life-changing news.

Leonard gives a candid public radio interview about the state of physics research. Amy and Bernadette commiserate over their unsung accomplishments.

Sheldon's anxiety over choosing the perfect wedding date spills over into his dreams. Bernadette's new coworker intrigues singletons Raj and Stuart.

Plagued by parenting doubts, Howard heads to the desert -- with Sheldon in tow -- to shoot off a model rocket. Penny bonds with Leonard's mother.

Sheldon and Raj don't react well when Amy enlists Howard's help on a project. Penny discovers the secret to managing a high-maintenance genius.

Wheeeeeeaton! Sheldon once again faces off with Wil Wheaton, this time over his beloved Professor Proton. Penny babysits Halley.

Sheldon's scientific snobbery alienates a colleague looking for help on a research project. Raj seeks advice after he reconnects with Ruchi.

Workplace distrust runs rampant when Leonard and Howard discover Sheldon's secret project, and Bernadette fears she's being undermined by a co-worker.

A potential Bitcoin payday leads the gang down memory lane, where Leonard learns how Penny really felt about him during one of their breakups.

A breakup affects the group. Wedding planning causes tension between Sheldon and Amy. A sought-after consulting gig leads Raj to a personal epiphany.

It's birthday time for Amy and Halley, but their celebrations don't go as planned. Leonard feels like an underachiever compared to his sibling.

Sheldon and Amy take a scientific approach to the task of choosing a best man and maid of honor by running secret experiments on their friends.

Sheldon boots Amy from the apartment so he can concentrate on his work. Meanwhile, Footprints on the Moon is back -- and rocking out in a big way.

A new romance lands Raj in the middle of a marital mess. A rekindled passion for string theory prompts Sheldon to ask Leonard and Penny for a favor.

Sheldon copes with conflicting feelings when Wil Wheaton debuts as Professor Proton. Leonard receives some eye-opening feedback on his book.

With Bernadette overdue and over being pregnant, her friends do their best to help get things rolling. Amy inadvertently reveals a secret to Howard.

An old nemesis holds the key to Sheldon and Amy's perfect nuptials. A sleep-deprived Howard and Bernadette face a big decision about the future.

When Penny announces that she's about to meet Bill Gates, the guys scheme to get in on the action. Bernadette's one-track mommy mind frustrates Amy.

Leonard clashes with Sheldon over control of the building's tenant board. Raj and Howard attempt to locate the owner of a high-end drone.

The guys tag along when Sheldon gets invited to the remote cabin of an eccentric genius. Amy's bachelorette party isn't what she expected.

Complications ensue when Stuart's comic book store suddenly becomes popular. Penny and Raj disagree over a celestial discovery.

While Amy shops for wedding dresses with Penny and Bernadette, Sheldon tries to raise $500 million to fund his latest scientific theory.

As Sheldon's wedding day approaches, his mother issues an ultimatum over his brother. Howard and Bernadette's kids spread an infectious disease.

A scientific breakthrough, "Star Wars" trivia and heartfelt declarations of love make Sheldon and Amy's wedding day a truly special occasion.

Sheldon and Amy's honeymoon hits a scheduling snag, Leonard upsets Penny with an unflattering comparison and Raj sparks a Twitter war with a celebrity.

While Sheldon and Amy try to decipher the meaning of Leonard and Penny's wedding gift, Raj seeks matchmaking help and Stuart gets dating advice.

Raj's dating compatibility questionnaire leads to a possible match -- and a revelation from Penny that surprises Leonard.

When Sheldon refuses to see his childhood best friend, the gang tries to figure out what led to their rift. Bernadette and Penny meet Raj's new flame.

Sheldon wants Amy to spend more time on their super-asymmetry project. Raj seems reluctant to have Howard join his planetarium show.

On Halloween, Penny and Leonard share very different recollections of their first kiss, while Howard's costume hurts Sheldon's feelings.

Bernadette finds the perfect hideaway to de-stress after work. Leonard faces a tough decision when he's tasked with handing out surplus grant money.

On the cusp of taking his relationship with Anu to a new level, Raj reverts to an old pattern. Sheldon attempts to forge a bond with Amy's parents.

While helping Sheldon and Amy track down citations for their super-asymmetry paper, Raj and Leonard make a startling discovery.

When Sheldon needs a pep talk after a work setback, Leonard breaks out the big guns. Bernadette helps Howard pursue his long-ago magician dreams.

The gang's planned paintball game turns out to be the perfect opportunity for the assembled couples to hash out their relationship issues.

Penny's ex Zack reappears with an unusual request for the Hofstadters. Raj tries to salvage his relationship with Anu.

Sheldon and Amy receive good news on their super-asymmetry project, but their happiness is short-lived. Bernadette taps Penny for a new role at work.

Sheldon helps Howard and Bernadette find a legal remedy to a neighbor's intrusive renovation. Leonard feels left out when Raj works on a new project.

To deliver on his promise to Zack, Leonard rebuffs Penny's advances. Meanwhile, Bernadette decides to brave weightlessness to prove Howard wrong.

The gang angles for an invitation to the hottest game in town: Wil Wheaton’s celebrity-studded Dungeons & Dragons night.

Hang time with the Wolowitz kids leads to a realization for both Leonard and Sheldon. Penny entertains an intriguing offer while at a drug conference.

To boost Sheldon and Amy's Nobel Prize campaign against their more PR-savvy rivals, the university hosts a laureate-packed reception in their honor.

A stressed-out Amy begins to crack under the pressure of being a Nobel Prize candidate and potential role model for young women in science.

Penny pushes Leonard to stop being such a people-pleaser. Raj grows frustrated when his scientific research is misconstrued.

Facing an ethical dilemma when they acquire information that could clear their path to the Nobel Prize, Sheldon and Amy seek advice from their friends.

The sudden attentiveness of Leonard's visiting mother confuses and delights him. Raj comes to a big decision about his future with Anu.

Big news brings big changes for Sheldon and Amy, but as one tries to embrace the shake-up, the other wants everything to stay the same.

In the series finale, secrets are revealed, hearts are broken and feelings declared as the gang's journey comes full circle.