Leonard and Penny finally get together, finding they still have a long way to go to understand each other. Howard starts seeing Bernadette, showing a suave side of himself that nobody knew was there.

!!Tropes in Series/TheBigBangTheory Season Three

* TheCloudcuckoolanderWasRight: ''Immediately'' after Leonard chews Sheldon out for pointing out Leonard's error in mixing highly explosive rocket fuel, the rocket fuel does indeed start going critical. And straight after, Sheldon correctly works out that putting it in a closed lift is the only option for containing the explosion - which Leonard again starts having a go at Sheldon for, saying they had plenty of time only for the explosion of the rocket fuel to literally happen mid-sentence. The only reason Leonard, Raj and Howard are ''actually alive'' in the present time is because of Sheldon.
* EmotionalRegression: Sheldon becomes like a child with Leonard and Penny as his parents in multiple instances.
* {{Hypocrite}}: in ''The Jiminy Conjecture'' Raj is about to call Sheldon out because it was inappropriate to talk about Leonard and Penny's "just fine" sex in front of them. [[WithFriendsLikeThese Even though the conversation only went in that direction because Raj and Howard were making fun of it themselves]].
* TheILoveYouStigma: Leonard saying it first and caught Penny off guard, leading into their break-up.
* MyGodWhatHaveIDone: Said by Howard and Raj once they realise that their little prank of fixing Sheldon up with a date has actually put him together with someone who is a good match.
* RelationshipUpgrade: Leonard and Penny, ''technically'' made official at the end of the second episode.
* ShutUpKiss: Penny is ready to date Leonard but he still doesn't know when to shut up, she helps him out there.
* SitcomArchNemesis: The beginning of Sheldon and Creator/WilWheaton's rivalry.
* SoreLoser: Sheldon, when he loses the game to [[SayMyName "WHEAAAATOOOOOOOON!!!!"]]
* TheirFirstTime: And it was weird.