Leonard and Penny's relationship has been a major subject in the series since the beginning of season one pilot episode. Almost all the season finales involve Leonard's relationship with Penny in some way.
Leonard's Initial Relationship With PennyEdit
Leonard began liking Penny as soon as she moved in during the pilot. He began running errands for her, such as going to get a TV from her ex-boyfriend Kurt. It wasn't until he got the courage to ask her out that they began dating. They had a few fights, but Leonard always liked her and they always managed to stay together. He was concerned about leaving her alone when he was arranged to go with the others to the North Pole. When he returned in Season 3 the first thing he did was go see Penny at her apartment, where she greeted him with a kiss. He gave her a preserved snowflake which she loved and they began dating. Leonard was very happy with Penny and told her in "The Wheaton Recurrence" that he loved her, which surprised her. Later in the episode Wil Wheaton breaks them up so his team could win a bowling match against Sheldon's team. Leonard was devastated by this break-up and, as Sheldon pointed out, cried about it. He even sniffed the pillow she slept on and listened to depressing and romantic songs. In Season 4 he began dating Priya and she insisted that he stop talking to Penny and letting her over to their apartment. Even though he was dating Priya, Leonard was reluctant to stop talking to Penny, but she agreed not to hang out with Leonard as much to help his relationship. At this point, Penny said goodbye to Leonard, though it didn't last. He has since broken up with Priya and gotten back together with Penny.
Penny's First Romantic Relationship With Leonard (2009-2010)Edit
When Penny first met Leonard, she only thought as him as a neighbor and a friend and had no romantic feelings for him at first. She asked favors of him and talked and visited him nearly every day. She ate take-out food with him and the others. Later on, she confessed she wanted to go out with a guy like him and with that, Leonard asked her out which she accepted. They went out a few times and fell out a lot.
At the end of Season 2, the episode "The Monopolar Expedition", Leonard and the others were arranged to go to the North Pole for three months. In that episode, she gave him a blanket with sleeves and hugged him, which made Leonard concerned about leaving her, but when he asked her about it, she said it was just a going away present. After he left and she closed the door, she whispered, "It means I wish you weren't going." When he returned at the beginning of Season 3, he went to see Penny, which she greeted him with a passionate kiss which Leonard happily returned. Leonard gave her a snowflake which she loved and they began going out again. After a quick trip to Texas to bring Sheldon home, the new couple finally consummated their relationship which they both described as weird.
Throughout season 3, they learned about each other and explored the limits of their relationship. There were some fights like Leonard belittling her for believing in psychics ("The Psychic Vortex") or Penny not telling him about her letting an ex-boyfriend stay in her apartment ("The Guitarist Amplification"), though there a lot of make-up sex and a lot of compromises mainly by Leonard. Sheldon was often frustrated with the constant presence of Penny within his inner circle and the couple many times were treating like they were his parents.
In the episode "The Wheaton Recurrence," Leonard told her he loved her, which surprised her because she wasn't ready for it, but they both got over it when they had to help Sheldon win a bet against Wil Wheaton in a bowling match. Wil Wheaton told Penny that it would be kinder to break-up with Leonard right away, which later revealed to be a trick to win the bet, but Penny had already broken up with Leonard, believing it would help him.
In Season 4, Priya wanted Leonard to stop hanging out so much with Penny. Penny agreed to it to help Leonard move on with his relationship. Penny hated Priya because of that and got upset with not talking to Leonard as much. At the end of Season 4, she admitted to Raj she regretted breaking up with Leonard. However, she is somewhat reluctant to start up a relationship with him again.
Penny and Leonard 2.0 (2012-2014)EditIn "The Recombination Hypothesis", Leonard decided to ask Penny out on a date and envisioned a possible ending of that date. In his fantasy, things did not go well the second time around, but he decided to go ahead and ask her out anyway, and Penny agreed to go. The episode ended with Penny envisioning herself very pregnant at a wedding of necessity with Leonard, a possible reason for her reluctance to go out with him again and her need to pick up her birth control pills. Leonard and Penny's fantasies regarding their possible reconciliation proved to have their merits when in the following episode, #101, (Season 5 Episode 14), "The Beta Test Initiation", it was shown that the two were contemplating to be official again. However, to avoid the mistakes from their first time together, they decided to take things slow by treating the relationship as a beta test, and even went to the length of presenting each other Bug reports to settle any issues.
Things seemed to be going well by the end of the episode, with Penny kissing Leonard at his doorstep after their date and at the shooting range. In "The Friendship Contraction", it was apparent that the two are definitely in a relationship again, albeit them taking things slow this time around, and the beta test that was still very much going on. During a blackout at the apartment, Leonard opted to hang out with Penny at her apartment and the two were about to make out when Sheldon interrupted them.
In "The Launch Acceleration", Penny suggested that they move up their relationship and get intimate; however Leonard ruined the mood when he asked her to marry him while they were having sex making their relationship feel weird to Penny.Season 6 starts with them on a date in "The Date Night Variable" where a lonely Raj crashes their date and insists that Penny tell Leonard that she loves him. Leonard wants to talk about their relationship; however she has had a hard day and wants to just hang out together. Penny is expressing doubts about her feelings for Leonard, though she claims to be happy with the relationship in "The Decoupling Fluctuation". She almost tells Leonard about her doubts and then ends up sleeping with him after looking into his sad eyes. In "The Higgs Boson Observation", Penny while spying with Amy sees Sheldon's pretty new graduate assistant Alex Jensen flirting with Leonard who is not responding. Later when Sheldon and Alex enter the apartment, Penny tells her about Leonard and their five year experiment together (relationship) and then she leads him off to her apartment for sex. In the Halloween theme episode "The Holographic Excitation", Penny gets advice from Bernadette that you get out of a relationship what you put into it and that maybe Penny should get more interested in Leonard's work (it is also revealed that, up until this point, Penny's view of their relationship had been one-sided in her favor). She visits his lab and is wowed by his holographic images and says that she sometimes forgets how smart he is. Penny heats up their relationship by starting to engage in sex in different locations, twice in his lab and twice in the TARDIS photo booth at the Halloween party.
In the episode "The 43 Peculiarity", Penny is working on a class oral project with an English student, Cole, who makes Leonard jealous. Leonard follows Cole down the stairs warning him about Penny's boyfriend, the "gang leader". Penny witnesses his deception and gets mad at Leonard telling him that he has nothing to worry about because she chooses to be with him and that he knows that she loves him. This pronouncement shocks both of them since Penny has never told Leonard that she loves him and she runs off scared before she breaks into tears. At the same time, Sheldon's assistant Alex Jensen is starting to hit on Leonard though he doesn't recognize her intentions. In "The Egg Salad Equivalency", Alex asks Leonard out to dinner after he expresses an interest in the Physics lecture she is going to and this attention really startles Leonard. Though it makes him feel good "to the bones" to have an attractive young woman interested in him, he tells everyone he still loves Penny and wouldn't do anything about it. He mentions Alex's actions to Sheldon who tries to talk to her about it and lands the whole gang in the Human Resources Administrator's office. He also didn't tell Penny about Alex's actions which made her feel really insecure about their relationship. Leonard apologizes by showing up at her door playing a little ditty on his cello.
In "The Spoiler Alert Segmentation", Leonard suggests that he move in with Penny after he again gets exasperated (again) with Sheldon. He asks her if she's all right with it, but she only agrees not to hurt his feelings and even tells Sheldon. She does try to get him admit that Sheldon can't get along without him. Amy plans to move in with Sheldon as roommates. When Amy confronts Penny since she can't move in with Sheldon, Leonard overhears the conversation. Penny tells him that he never asked her if she was ready. Then Amy and Penny go off to drink and talk about their jerky boyfriends and Leonard ends up back in Apartment 4A. Amy also scares Penny when in anger says that she and Penny should move in together. In "The Tangible Affection Proof", Leonard takes Penny out to dinner for Valentine's Day. Penny feels that all the efforts never meets the the expectations and she will end up disappointed. At dinner, Penny sees an old boyfriend proposing to the girl that broke them up. Leonard again tries to propose and Penny stops him. They begin to argue in front of Howard and Bernadette who have their own issues that night. After they barely say good night, Leonard tells Penny that she ruined the whole evening. Penny finally admits that she has commitment issues. She is so happy right now that she knows they are going to get married and since that relationship is forever that scares her. Leonard then puts the responsibility of proposing on her and that she should do it when she's ready. In the end, she does ask him to be her valentine.
In "The Closure Alternative", Penny was concerned about the passion Leonard showed for science, comics books, and various television shows while she had no passion in her life. Her dreams had always been to become a famous movie star and live a glamorous life. Anything less than that she felt was settling. Her epiphany came that she is passionate about her boyfriend Leonard and all her wonderful friends.In "The Bon Voyage Reaction", Leonard takes a job working on a Stephen Hawking expedition in the North Sea for four months over the summer. Penny will miss him, but knows that it is a good opportunity and sends him off. At the airport, she is fussing over him like a wife sending her husband off on a business trip. She also has to watch Sheldon over the summer, too.
In "The Hofstadter Insufficiency", Leonard hurts Penny because he seems to be having such a great time on the ship, she thinks that he is not even missing her. In "The Deception Verification", Leonard makes up for it by showing up early and hides in her apartment so that they can spend time together a couple before telling the gang that he's back. It works until Amy and Sheldon find them together after they think that Penny is cheating on Leonard.
In "The Raiders Minimization", Penny purchases a psychology that Beverly Hofstadter has written about all his problems growing up for a night school class. Leonard finds out that Penny will do things he wants to do [ditch going to a sports bar, watch geeky shows, have sex] and uses her. Leonard mentions it to Howard, so his actions make it back to Penny. She dresses up for sex tempting him and then for revenge makes him skype with his mother to discuss his actions much to Leonard's disgust.In "The Romance Resonance", Howard makes a romantic gesture to Bernadette by writing her a song. Leonard mentions that Penny never does anything like that, except for sex which doesn't count. Penny is determined to romance Leonard. Raj can only suggest that she cook for him or reenact a scene from a romantic movie. Finally after a candlelight dinner, Penny puts on some romantic music, spreads rose petals into her neatly cleaned bedroom and presents Leonard with a first edition of his favorite book from when he was growing up, The Hitchhiker Guide to the Galaxy. Unfortunately, Leonard had already purchased the book after they had seen it in a used bookstore together. Penny gets upset telling him about all the thoughtful things he had done for her and shows him her collection. An airplane ticket, a rose given to her "just because" and the eleven page letter he wrote her after the first time they slept together. Leonard was very touched that she kept all these things. He then kisses her, showing that Penny did do something romantic.
In "The Thanksgiving Decoupling", Penny reminisces about a Thanksgiving she had in Las Vegas with former boyfriend Zack Johnson which included one of those "silly fake weddings". Penny appears devastated when her friends inform her that the wedding was real and she is Mrs. Zack Johnson. Penny and Leonard argue about how quickly she should get her annulment so Penny invites Zack over to their Thanksgiving dinner at Howard's mother. Zack appears as dimwitted as ever telling them that breaking up can be hard on the kids which they don't have. Finally, Penny and Leonard make up and she tells him that the next time she gets married it will be for real, for love (jokingly) or for money.In "The Hesitation Ramification" and "The Occupation Recalibration", Penny gets a part in the TV series NCIS and is very disappointed when her scene is cut and not aired. Frustrated and tipsy, she sees her life crumbling when Leonard reminds her that she still has him. She agrees with him and probably to show some advancement in her life, she kneels down and proposes to him. All Leonard can utter is "Umm", much like when he wouldn't succumb to her drunk advances after her Halloween party in "The Middle Earth Paradigm". Penny gets very upset since she doesn't think he wants to marry her. After she storms out, Leonard is afraid to ask her if their relationship is now over. The next day/episode he does visit Penny who assures him that they are still together and that he did the right thing not agreeing to her proposal because she was a mess. Now she has rethought her career and decides to quit the Cheesecake Factory and focus all of her time on acting. Leonard does support her though he is obviously worried about her.
In "The Table Polarization", the gang wants to add a dining room table to Apartment 4A which Sheldon objects to. Penny gets Leonard to pick out a dining set that she likes and gets Leonard to stand up more against Sheldon. Sheldon objects to Penny changing Leonard to stand up against him. Penny points out that Amy has changed Sheldon who agrees and then decides to break up with Amy.
In "The Mommy Observation", Raj has a murder mystery night where they speculate where they will be twenty years in the future.The couple start thinking about how they will deal with each others success. Penny figures that Leonard will follow her around if she is famous and making a lot of money while Leonard thinks that he might be tenured at a university and can move around. Finally Stuart ends the argument saying that he thinks that they have the strongest relationship he knows. Penny brought Leonard out of his shell and Leonard got Penny thinking about her place in the bigger picture.
The Engagement (2014-Present)EditIn "The Gorilla Dissolution", Leonard and Penny get back in her apartment after getting fired from her movie. Penny wants to start making smarter decisions about her life. She says that they could get married and Leonard asks her to be serious. Leonard asks her if he is a smart decision, like choosing a healthy boring bran muffin. Penny doesn't care what pastry he is because she is CHOOSING HIM. Leonard is still talking about being a pastry like a Cinnabon or a Strawberry Pop Tart that she is excited about. Penny tells him to forget about it. Leonard does want to marry her, but feels that she is just feeling sorry for herself because she was fired. Penny explains that it may seem that way, but getting fired made her think that fame and fortune is not what is going make her happy. Leonard wants to know what she needs. "You, you stupid Pop Tart!" Leonard finally says that he guesses that he is in, which also bothers Penny. Leonard then retorts that it is an excited "I guess I'm in" and they agree that they are engaged which seems somewhat anti-climatic. To change the mood, Leonard pulls a diamond ring out of his wallet that he has had for a couple of years, gets down on one knee and asks Penny formally. Penny says "Oh my God, yes" and he slips the ring on her finger that still has ape hair glued to it and they embrace.
In "The Status Quo Combustion", Leonard and Penny announce their engagement; however, the gang is more excited about Raj and Emily hooking up. Leonard goes searching for the missing Sheldon and finds him at the railroad station leaving time to think about all the changes in his life. Leonard wants him to come home, but Penny convinces him that he should let Sheldon go.
In the early part of season 8, the engaged couple is doubting their mutual connection and are scared of the idea of marriage, but are still commited to each other.