The Big Bang Theory

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Watch The Big Bang Theory Season 4 full episodes online, free and paid options via our partners and affiliates.

New Roomies
Watch The Big Bang Theory Season 4 Episode 24
"The Roommate Transmogrification"
Original Air Date:

Raj moves in with Sheldon on the fourth season finale of The Big Bang Theory. This takes Penny by surprise.

Kunal Nayyar Promo Pic
Watch The Big Bang Theory Season 4 Episode 23
"The Engagement Reaction"
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When Howard finally breaks the news to his mom that he's engaged to Bernadette, it lands her in the hospital.

Raj in Action
Watch The Big Bang Theory Season 4 Episode 22
"The Wildebeest Implementation"
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Raj attempts to cure his social anxiety disorder while Penny uses Bernadette to spy on Leonard and his girlfriend.

Sheldon Busts a Move
Watch The Big Bang Theory Season 4 Episode 21
"The Agreement Dissection"
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When Priya uses her lawyer skills to pick apart the roommate agreement, the girls take Sheldon dancing on this episode of TBBT.

Sheldon and Amy Photo
Watch The Big Bang Theory Season 4 Episode 20
"The Herb Garden Germination"
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Sheldon and Amy spread gossip this week. Elsewhere, Howard takes a big step in his relationship with Bernadette.

Nerds on a Mission
Watch The Big Bang Theory Season 4 Episode 19
"The Zarnecki Incursion"
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Someone has the gall to hack into Sheldon's online game account this week. The guy go on a search to find out who would dare do such a thing.

Hi, Couple!
Watch The Big Bang Theory Season 4 Episode 18
"The Prestidigitation Approximation"
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Wolowitz baffles Sheldon this week with a magic trick. Elsewhere, Leonard realizes that there's a problem with him dating Priya.

The Toast Derivation Scene
Watch The Big Bang Theory Season 4 Episode 17
"The Toast Derivation"
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Sheldon struggles with a realization on this episode: Leonard who is actually the center of the social group.

The Cohabitation Formulation Scene
Watch The Big Bang Theory Season 4 Episode 16
"The Cohabitation Formulation"
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Wolowitz considers going all the way with Bernadette this week. Elsewhere, Leonard rekindles his relationship with Raj's sister.

The Benefactor Factor Scene
Watch The Big Bang Theory Season 4 Episode 15
"The Benefactor Factor"
Original Air Date:

A donor is willing to give Leonard a lot of money this week. In exchange for sex from him, that is.

Koothrappali Fantasy
Watch The Big Bang Theory Season 4 Episode 14
"The Thespian Catalyst"
Original Air Date:

Sheldon gets acting lessons from Penny on this episode. Elsewhere, Koothrappali fantasizes about his best friend's gal.

Rick Fox on The Big Bang Theory
Watch The Big Bang Theory Season 4 Episode 13
"The Love Car Displacement"
Original Air Date:

There's tension at a hotel this week. That's because the group runs into Bernadette's ex-boyfriend during a science event.

The Bus Pants Utilization Scene
Watch The Big Bang Theory Season 4 Episode 12
"The Bus Pants Utilization"
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Leonard gets an idea for a smart phone application on this episode. How does that go? Find out now.

As the Justice League
Watch The Big Bang Theory Season 4 Episode 11
"The Justice League Recombination"
Original Air Date:

The guys find a use for Penny's boyfriend this week, as they enter a costume contest and they go as the Justice League members.

Penny, Bernadette and Amy
Watch The Big Bang Theory Season 4 Episode 10
"The Alien Parasite Hypothesis"
Original Air Date:

Amy realizes she has sexual feelings for Penny's ex on this episode. That's awkward. Meanwhile, Koothrappali and Wolowitz attempt to prove who would be the better superhero.

Keith Carradine on TBBT
Watch The Big Bang Theory Season 4 Episode 9
"The Boyfriend Complexity"
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Penny asks Leonard to fib to her father this week. Elsewhere, Howard, Raj and Bernadette go for an all-nighter with a telescope.

Return of Wil Wheaton
Watch The Big Bang Theory Season 4 Episode 8
"The 21-Second Excitation"
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Wil Wheaton is back this week! He causes problems for the guys when they try to see a movie. Elsewhere, Penny and Bernadette invite Amy to a sleepover.

Pretty, Funny Guest Star
Watch The Big Bang Theory Season 4 Episode 7
"The Apology Insufficiency"
Original Air Date:

Sheldon places Wolowitz's security clearance in danger this week. How so? By answering questions from an agent played by Eliza Dushku.

The Irish Pub Formulation Scene
Watch The Big Bang Theory Season 4 Episode 6
"The Irish Pub Formulation"
Original Air Date:

A major secret abounds this week, as Leonard keeps quiet about an affair with Raj's sister. Will Sheldon keep the secret?

Amy with Sheldon
Watch The Big Bang Theory Season 4 Episode 5
"The Desperation Emanation"
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Amy wants to introduce Sheldon to her mother on this episode. Meanwhile, Leonard is down on himself as he comes to terms with the fact that all the other guys have girlfriends.

Big Bang Guest Stars
Watch The Big Bang Theory Season 4 Episode 4
"The Hot Troll Deviation"
Original Air Date:

We learn of an embarrassing secret about Wolowitz this week. How is that for a tease?!? Read our recap to learn more.

The Zazzy Substitution Scene
Watch The Big Bang Theory Season 4 Episode 3
"The Zazzy Substitution"
Original Air Date:

The focus of this week's episode: Sheldon's search for an alternative to human companionship. Read on to see how that goes.

A Sheldon Diagram
Watch The Big Bang Theory Season 4 Episode 2
"The Cruciferous Vegetable Amplification"
Original Air Date:

By the time he downloads his consciousness into a robot body, Sheldon realizes he'll be long gone. As a result, he attempts to make himself live longer.

Feelin Good
Watch The Big Bang Theory Season 4 Episode 1
"The Robotic Manipulation"
Original Air Date:

Penny tags along for Sheldon's first date on the fourth season premiere. Elsewhere, Wolowitz discovers a new use for a robotic arm.

The Big Bang Theory Season 4 Quotes

Penny: Hey, Sheldon, did you change your Wi-Fi password again?
Sheldon: Yes, it's "Penny, get your own Wi-Fi." No spaces.

Leonard: Hi. I'm Leonard. You are beautiful. You pop, sparkle and buzz electric. I'm going to pick you up at eight, show you a night you will never forget.
Raj: Where are we going?