When the University reassigns Sheldon’s parking spot to Wolowitz, their fight affects the whole gang.

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

Wolowitz struggles with moving out of his mother’s house. Meanwhile, Sheldon is caught in the middle of an argument between Amy and Wil Wheaton.

Sheldon’s relationship with Stephen Hawking is threatened over a game of “Words with Friends,” and Penny secretly enrolls in a class at the local college.

The gang celebrates Halloween at Stuart’s comic book store. Meanwhile, Leonard seduces Penny with science.

When Wolowitz returns from space, he doesn’t get the hero’s welcome he expected. Meanwhile, Game Night turns into a battle of the sexes.

Amy feels threatened when Sheldon hires a young female assistant, and the pressure of being in space takes its toll on Wolowitz.

When Sheldon learns that Penny is thinking about breaking up with Leonard, he tries to intervene. Meanwhile, in space, the other astronauts pick on Howard.

With his friends on dates, Raj must face his loneliness. Also, Wolowitz is caught in an argument between Bernadette and his mom, even while he’s in space

The fifth season ends with Howard and Bernadette deciding to get married before his NASA mission, causing the gang to scurry into overdrive in an effort to stage the wedding. NASA astronaut Mike Massimino has a cameo as himself.

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.

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

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

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.

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

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.

Penny is horrified when Amy gives her a gift: a huge, quite horrible painting of the two of them. With no good way to avoid displaying it, she only hangs it up when Amy is over. When Amy catches her taking the painting down, she’s embarrassed and angry until Penny lies and says the gift made Bernadette jealous.

When the deranged Professor Rothman is forced to retire, both Sheldon and Kripke vie for his office. President Siebert refuses to resolve the dispute, so Leonard arranges a one-on-one basketball game to decide (since they’re both equally bad at sports). Neither one can even make a single basket, so they end up deciding by seeing who can bounce the ball the highest. Sheldon wins; unfortunately, the office is not what he’d hoped for: the thermostat is located in the office of a professor going through the hot flashes of menopause (thus Sheldon is too cold), the mockingbird outside his window is off-key with the annoying windchimes, the perpetually naked Professor Rothman refuses to vacate, and the Geology Department upstairs makes too much noise. Finally, Sheldon gets his head stuck in the wall in an existing hole, after which Leonard takes his picture before he goes for help.

When Sheldon is forced to take his vacation, he goes to work with Amy in her neurobiology lab.

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

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, in the form of Siri on his new phone. Meanwhile, Sheldon decides to start a YouTube series entitled “Sheldon Cooper presents Fun with Flags” with the help of Amy.

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

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 must face his fears after being contacted by his high school tormentor.

When Stuart asks Amy out on a date, Sheldon must confront his feelings and consider where his relationship with Amy is going.

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.

Amy becomes heartbroken when she discovers that Penny and Bernadette went wedding dress shopping without her.

A cute comic book artist puts Leonard and Priya’s relationship to the test, while Sheldon tries to scare the guys for Halloween.

Sheldon’s mother, Mary Cooper, comes to visit, but Sheldon is annoyed that she also spends time with the rest of the gang, instead of catering to his every demand.

Sheldon and Leonard get invited to a party at Wil Wheaton’s house, and Howard gets an out-of-this-world opportunity.

Penny plays Matchmaker for Raj, which results in him finding a girl he is comfortable talking to.

Leonard and Amy get to know each other better, while Howard and Bernadette spend the weekend with Mrs. Wolowitz.

A fight between Sheldon and Penny leaves Amy caught in the middle, while Leonard tries to spice up his long-distance relationship with Priya.

Penny is worried with how damaged her friendship with the guys will be in the aftermath of her sleeping with Raj while Sheldon becomes the leader of the paintball team.

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

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

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

When Leonard spends too much time in the shower with Priya, Sheldon charges Leonard with two violations of the roommate agreement. However, before he can get too far, Priya uses her skills as a lawyer to nullify the charges due to the agreement’s vague wording, much to Sheldon’s dismay. When the guys take advantage of Priya’s skills in order to eat Greek food on pizza night, Sheldon goes to Penny, who invites him to a girls’ night out with Amy and Bernadette, which Sheldon agrees to after Penny mentions that they may be talking trash about Priya. After the girls drink some cocktails, they decide to take Sheldon dancing, which Sheldon reluctantly goes along with. After dancing, Sheldon takes an intoxicated Amy back to her apartment and as well as talking about Priya, meets a monkey who is addicted to smoking cigarettes. Amy tells Sheldon not to give in to Priya’s law skills, before kissing him and going to her bathroom to vomit.

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

Sheldon’s online-game account is hacked by Todd Zarnecki, who then proceeds to steal all his items prompting the guys to go on a quest to retrieve them. Penny, Bernadette and Amy discuss how Penny groomed Leonard to be willing to try various things and more adventurous boyfriend… for some other woman — Priya.

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