The Big Bang Theory - Season 4

This season the Big Bang gang’s romantic universe expands. On the rebound from Penny, Leonard falls into the arms of Raj’s sister Priya. Sheldon gets a girlfriend, or rather a friend who is a girl: Amy, a dour neurobiologist who declares herself besties with Penny. Howard and Bernadette heat up. And so do Raj and Bernadette (at least in Raj’s Bollywood daydream).

24 Episodes

The Robotic Manipulation

Season 4 - Episode 1

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

The Cruciferous Vegetable Amplification

Season 4 - Episode 2

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

The Zazzy Substitution

Season 4 - Episode 3

The guys are concerned as Sheldon searches for an alternative to human companionship.

The Hot Troll Deviation

Season 4 - Episode 4

An embarrassing secret of Wolowitz's comes to light, while Sheldon and Raj have a small war at work.

The Desperation Emanation

Season 4 - Episode 5

Leonard realizes he’s the only one without a girlfriend, while Sheldon wants to get rid of his.

The Irish Pub Formulation

Season 4 - Episode 6

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

The Apology Insufficiency

Season 4 - Episode 7

Sheldon's answers during an FBI interview put Wolowitz's security clearance in jeopardy.

The 21-Second Excitation

Season 4 - Episode 8

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

The Boyfriend Complexity

Season 4 - Episode 9

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

The Alien Parasite Hypothesis

Season 4 - Episode 10

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

The Justice League Recombination

Season 4 - Episode 11

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

The Bus Pants Utilization

Season 4 - Episode 12

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

The Love Car Displacement

Season 4 - Episode 13

Bernadette runs into her ex-boyfriend while attending a science event with Wolowitz.

The Thespian Catalyst

Season 4 - Episode 14

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

The Benefactor Factor

Season 4 - Episode 15

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

The Cohabitation Formulation

Season 4 - Episode 16

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

The Toast Derivation

Season 4 - Episode 17

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

The Prestidigitation Approximation

Season 4 - Episode 18

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

The Zarnecki Incursion

Season 4 - Episode 19

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 re...

The Herb Garden Germination

Season 4 - Episode 20

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

The Agreement Dissection

Season 4 - Episode 21

When Leonard spends too much time in the shower with Priya, Sheldon charges Leonard with two violations of the roommate agreement. However, ...

The Wildebeest Implementation

Season 4 - Episode 22

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

The Engagement Reaction

Season 4 - Episode 23

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

The Roommate Transmogrification

Season 4 - Episode 24

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