Howard is selected to be part of a crew to go to the International Space Station. Sheldon and Amy officially become a couple. Leonard and Penny are tired of fighting their feelings for each other and get back together.

!!Tropes in Series/TheBigBangTheory Season Five

* AccidentalInnuendo: InUniverse. A running joke in the 100th episode involves Sheldon dropping these while playing ''TabletopGame/SettlersOfCatan''.
--> '''Sheldon''': I want to build a road, but I need wood. Either of you fellas have wood? (Raj and Howard giggle) I don't understand the laughter. The object of ''Settlers of Catan'' is to build roads and settlements. To do so requires wood. Now, I have sheep, I need wood. Who has wood for my sheep? [..] Come on, I just want wood. Why are you making it so hard?
--> (later) And now that I have some wood, I will begin the erection of my settlement.
--> '''Raj''': (aside, to Howard) Okay, he's got to be doing this on purpose.
** It's a very common joke for '''Settlers''' in real life as well.
* BewareTheNiceOnes: Played with. Bernadette is understandably ''pissed'' when she finds out Raj has been writing love poems about her, yet she is still nice about it.
-->'''Raj:''' Bernadette?
-->'''Bernadette:''' WHAT?
-->'''Raj:''' Do you think I have a shot with Penny?
-->'''Bernadette:''' OF COURSE YOU DO. YOU'RE A CUTIE-PIE! ANY GIRL WOULD BE LUCKY TO HAVE YOU! (slams door)
* BullyTurnedBuddy: PlayedWith; Leonard's former high school bully tracks him down. Leonard thinks he might be there to apologize for his bullying ways, but it turns out that the bully has an idea for an invention that he wants Leonard's help with. The bully doesn't even realize that what he had done to Leonard was bullying, he is under the impression that they were just playing around.
* CrucifiedHeroShot: Done by Sheldon in a game of paintball, a direct {{homage}} to ''Film/{{Platoon}}''.
* DaydreamSurprise: The entirety of "The Recombination Hypothesis" was a daydream by Leonard trying to figure out his feelings for Penny and their future. The relationship fails, but he still decides to ask her out again in real life.
* EntitledBastard: In ''The Wiggly Finger Catalyst'' Penny breaks up Raj's relationship with Emily, even though Raj was fully aware that Emily was a GoldDigger and perfectly okay with it. After Penny splits them up by telling Raj's parents, she tells him that she wants a big tip, since he's rich, at the end of the episode.
* HeelRealization: Bernadette surprised herself when she realized she was wrong to try to keep Howard from taking his chance at realizing his dream.
** Penny when she realized she was a bully in school and tried to apologize to the people she bullied.
* LongList: The list of things that were stolen from Sheldon and Leonard's apartment, most of which were video games.
* MildlyMilitary: Sheldon gives himself the Paintball rank of Captain, citing Kirk, Crunch and Kangaroo as examples. He sews Army Captain's bars to his uniform, but the three he references are Navy/Coast Guard Captains, the equivalent of Army Colonels.
* MutualDisadvantage: To decide who gets Prof. Rothman's office, Sheldon and Barry play a one-on-one game of basketball, under the notion that they are equally bad at sports, putting them on an even field. It works too well, in fact, as neither manages to score once after 45 minutes.
* MyFriendsAndZoidberg: Sheldon refers to the rest of the group as his "three friends and one treasured acquaintance", who turns out to be Howard.
* OOCIsSeriousBusiness: Howard kicking Bernadette out of the house, ''without wanting sex with her'' is a sign that he is '''really''' not happy about Bernadette going behind his back and telling his mother that he was picked by NASA to go into space.
* PaintballEpisode: After Sheldon's DeathSeeker action in being a horrible leader, he ended up inspiring the guys to take back the game and they won the inter-department paintball game for the first time.
* RelationshipUpgrade: It was a real shock when Sheldon asked Amy to make their relationship official.
** Another one for Leonard and Penny who begin dating again after "The Recombination Hypothesis." The previous season heavily hinted that Leonard and Penny still cared about each other and they officially begin dating again.
* RewatchBonus: Give "The Recombination Hypothesis" a 2nd look, and you'll spot some subtle clues throughout that most of the episode is [[spoiler: a daydream Leonard is having.]] The most telling clue being that Sheldon is seen ''flirting'' with Amy at one point.
* ThirdActMisunderstanding: The season opens with everyone believing that Penny and Raj slept together.[[spoiler: Raj later reveals to Penny that they didn't actually sleep together and instead fell asleep after Raj had trouble putting on the condom.]]
* UnwantedGiftPlot: Amy gives Penny a tacky painting of the two of them, insisting that it be displayed prominently in her living room. It is supposed to be hung on the fourth wall, which is why it hasn't been seen since.
* WackyMarriageProposal: Penny was not pleased when Leonard asked that in bed.