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

Leonard, Sheldon and Howard give lectures on science to junior high students. The girls ditch work to go to Disneyland. Raj devises a date for Lucy that fixes their social…

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

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.

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

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.

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.

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

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

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

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.

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

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.

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….

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…

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…

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…

Sheldon battles Kripke for a coveted office at the university. Penny receives a very unusual gift from Amy.

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, 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.

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…

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

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.

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