When you think of “The Big Bang Theory” the first thing that comes to mind is “geek” and that is part of what it is about; 4 geeks that can’t relate to “normal” people in the world trying to fit in and not really succeeding. At first; eventually they manage to figure out how to “act” around non-geeks and make them like them.
This brings us to the Leonard and Penny relationship that has existed since the pilot episode aired six seasons ago. Every episode (except a small few) includes their romantic relationship directly or how their feelings for each other interfere in their current lives. I included a list of 10 episodes that were most important in relation to their relationship; not an easy task with how many shows there are about them!
1. "The Tangerine Factor" (Season 1, Episode 17)
When it comes to Leonard and Penny, the first season in its entirety is a setup for this episode. In the first sixteen episodes they flirt with each other, Leonard is more obvious while Penny is able to be more subtle about it, so we know that they are both interested in each other and it is not one-sided. This episode is (obviously) important to their relationship since Leonard finally asks Penny out on a date and Penny accepts. Not only is this episode mark an important step in their relationship, the episode is important since a lot of the episodes in the following season are possible because of the fact that they went out on a date.
2. "The Codpiece Topology" (Season 2, Episode 2)
Penny has a new boyfriend and when Leonard discovers this he decides to rekindle a relationship with Leslie Winkle. This doesn’t directly affect Leonard or Penny directly, but what it does is show us that they are not yet over each other and still have feelings for each other. When they see each other in the hallway with their respective new significant other’s, they each try to outdo the other in order to show that they are over the other. Leonard passionately kisses Leslie and when Penny sees this, tries to one-up Leonard by being more passionate with her boyfriend. Once Leonard is gone, Penny pushes the guy aside, tells him goodnight and closes her apartment door behind her leaving him alone in the hallway.
3. "The Classified Materials Turbulence" (Season 2, Episode 22)
Stuart is going on a second date with Penny, much to Leonard’s disappointment. He is so jealous about the fact that Stuart is going on a date with her again that he goes so far as to give him bad advice in the hopes of having his advice backfire and Penny losing interest in Stuart. Fortunately it seems that Leonard didn’t have to go so far since during their date Penny called Stuart by Leonard’s name as they were making out. This, unsurprisingly made Leonard extremely happy and renewed the possibility of the two of them potentially dating again.
4. "The Monopolar Expedition" (Season 2, Episode 23)
Leonard is leaving for the North Pole and Penny gives him a gift before he leaves. The importance here isn’t so much the gift, it’s the fact that Penny is surprised that Leonard is leaving and never told about it before hand and is acting like she will genuinely miss him while he’s gone. When she’s confronted about her feelings by Leonard before he leaves, she doesn’t have the courage to tell him what she really feels towards but rather says how she feels about it to her door after she’s closed it saying that she wishes that he wasn’t going.
5. "The Electric Can Opener Fluctuation" (Season 3, Episode 1)
Anyone who has watched the show knows why this one is relevant to their relationship since this is the episode where they finally get together. Penny is unable to hide her joy at seeing him back from the North Pole and literally jumps on him the instant she opens the door and sees him. Even though they finally got together like they wanted, the added aspect of their relationship has made their relationship rather awkward.
6. "The Wheaton Recurrence" (Season 3, Episode 19)
This is the next significant episode in their relationship. Leonard tells Penny that he loves her and Penny is only able to say thank you in response. Later on in the episode, when they are bowling, Leonard reacts to Penny saying that she loves chilly cheese fries, which makes Penny walk out. When they go back and play another game of bowling, Wil Wheaton speaks with Penny and makes her realize that she is not being fair to Leonard, she apologizes to him telling him that she can’t do this anymore and walks out again, effectively breaking up with Leonard.
7. "The 21-Second Excitation" (Season 4, Episode 8)
Season 4 had Leonard dating Raj’s sister Priya throughout much of the season, which affected Penny more than she thought it would. The importance of this episode isn’t with any interaction between Leonard and Penny, it is between Penny, Bernadette and Amy. During their girl night, Amy asks Penny how she would feel if another woman were to date Leonard because he was, as she had put it a “great catch”. Penny is completely taken aback by the question and her feelings for Leonard return to the surface. Not wanting to deal with the feelings, she storms out of the room and into her bedroom.
This is the only episode from season 4 on this list since the majority of the season sees Leonard dating Priya and Penny not hanging out with the guys as often as she would because of it. The only real revelation about their relationship from season 4 is that Penny regrets breaking up with Leonard.
8. "The Recombination Hypothesis" (Season 5, Episode 13)
The 100th episode has Leonard asking Penny out on a date. The whole episode is Leonard thinking of what would happen if they did start seeing each other again and so the only “real” non-imagined event of the episode is at the end when he actually does ask her out again and Penny asks him if he’s thought this out before actually asking her. When he says that he did, Penny agrees to go on another “first date” with him.
9. "The Launch Acceleration" (Season 5, Episode 23)
In a previous episode, they both agreed that their relationship was in the “beta test” and now Penny thinks that things are progressing well enough to move onto the next level. What happens in this episode is that Leonard proposes to Penny in the middle of sex. Penny is shocked at the proposal and Leonard tries to apologize for the incident but it doesn’t work. Penny later tells Leonard no to the marriage proposal and their relationship continues. Leonard is ready to move to the next stage of their relationship while we see that Penny is still holding back.
10. "The 43 Peculiarity" (Season 6, Episode 8)
Leonard does not like the idea that Penny’s partner for her class assignment is a man. When Penny’s partner comes to her apartment to work on the project, Leonard spies on them and later walks down with him in order to advise him to not try anything with Penny because her boyfriend wouldn’t like it. Penny, as expected, takes offense to how he is acting towards the entire situation. This isn’t what made this episode make the list, what puts it here is how Penny dealt with the situation. Penny, for the first time, admitted that she loves Leonard. Leonard was shocked and happy to hear it while Penny seemed like she didn’t expect at all to blurt it out and told Leonard to leave it at that and to not bring it up again because they will both become emotional. Leonard agrees. Even though we all had an idea that Penny did love Leonard, the fact that she acknowledge those feelings out loud was a great moment and even though they may be at slightly different places in the relationship (ie: Leonard wants to get married and Penny doesn’t) we now know that at least they both feel strongly for each other.
Aside from these 10, there have been dozens of other episodes that revolved around their relationship. Some showed they had/always had feelings for each other , such as Penny getting jealous that Leonard was dating other women or vice versa with Leonard being jealous of Penny dating other men. Some also drove a wedge between them. For instance, one episode saw Leonard being unsure if he could keep dating Penny knowing that she fully believed in psychics. Overall, it is safe to say that the majority of the episodes were plot dependent on their relationship and the episodes not only provided an insight on their relationship and their problems, they allowed us to see two individuals mature through the years to reach the level of intimacy that they now share in their relationship.