The Season 9 episode “The Opening Night Excitation” does something incredibly clever, even for “The Big Bang Theory” — it combined two major events in a way that actually made sense, forcing Sheldon to choose between seeing “Star Wars: The Force Awakens” or spending Amy’s birthday with her and, as he put it, have “coitus” with her for the very first time. If you’re at all familiar with Sheldon Cooper, you know that he can be, to put it lightly, incredibly selfish. There’s any number of ways that Sheldon could completely botch this situation and leave Amy in the lurch, but he puts her first and the two finally consummate their incredibly slow-moving relationship while the rest of the gang goes to see “The Force Awakens.”

From Penny and Bernadette’s ecstatic reactions to Sheldon announcing his intention to have “coitus” with Amy for her birthday to the appearance of Bob Newhart’s Professor Proton (in a dream Sheldon’s having) to Bernadette and Penny’s ridiculous scheme to “prepare” Amy for her night with Sheldon, “The Opening Night Excitation” is great from beginning to end. Add in that final shot that juxtaposes Sheldon and Amy’s post-coital bliss with the rest of the guys staring at the “Star Wars” credits in awe, and you’ve got an endlessly rewatchable episode.

This is going to be a bit of a recurring theme on the list, but the most important relationship on “The Big Bang Theory” isn’t romantic at all — it’s the friendship between Sheldon and Penny. In the Season 3 episode “The Adhesive Duck Deficiency,” the biggest thing that happens is that Penny slips and falls in the shower and gets hurt; because she lives alone, she has to just keep yelling for help until someone (specifically, Sheldon) hears her. (Howard, Leonard, and Raj are out of town to try and see the Leonid meteor shower at a remote campsite.) When Sheldon finds Penny, he’s not immediately helpful — telling Penny what she probably specifically injured instead of, you know, helping her immediately — but he ultimately tells her, “Never let it be said that Sheldon Lee Cooper ignored the pleas of a damsel in distress.”

Sheldon, who hates driving, must drive Penny to the emergency room … and notably, he even stays with her for the entire visit to ensure that she’s not all by herself and injured. When Sheldon helps Penny home, he even, at her urging, sings “Soft Kitty” to her (put a pin in that) while she’s on pain medication with her arm in a sling so that she can go to sleep. Sheldon isn’t often sweet, but any episode where he’s sweet to Penny specifically is super rewatchable.

One of the very best episodes of “The Big Bang Theory,” the Season 7 installment “The Scavenger Vortex” does split up the main gang — but by creating super-unlikely character pairings, it ends up becoming a near-perfect episode of the show overall. Raj, annoyed that all of his friends ditched his murder mystery dinner, decides to torment all of them with an intensely involved scavenger hunt based on the kinds of super-difficult hunts that the Massachusetts Institute of Technology famously hosts. Though the gang is excited as they’re split into teams — Sheldon and Penny, Leonard and Bernadette, and Howard and Amy — they soon realize that Raj has designed one of the most insanely involved scavenger hunts of all time, and they all start to basically lose their minds hunting for each object and blue.

While Raj is delighted watching the three teams try to solve his puzzle — even telling them at one point, “Do you see what I did? The first puzzle… is a puzzle! Oh, my God, how adorable is that? I wish I had a friend like me” — Howard and Amy bond over their shared love of Neil Diamond and Leonard realizes that Bernadette’s competitive streak is quite a bit stronger than anyone initially thought. Plus, the conclusion of the scavenger hunt is phenomenal. “The Scavenger Vortex” is a great episode of “The Big Bang Theory,” and it’s endlessly rewatchable.

“The Big Bang Theory” features some genuinely phenomenal guest stars throughout its long run, including the late Stephen Hawking and other luminaries like Mark Hamill (and actually, we’ll come back to his whole deal later). Perhaps its biggest “get,” though, was Marvel Comics icon Stan Lee, who honored the show by appearing in the Season 3 episode “The Excelsior Acquisition.” In said episode, the whole gang finds out that Lee, who passed away in 2018, is going to be signing comics at their local store; unfortunately for Sheldon, he can’t attend because he has to go to court to fight a red light ticket. (Hilariously, he ran that red light while he was bringing Penny to the hospital in “The Adhesive Duck Deficiency.”) As usual, Sheldon completely gets in his own way during his hearing and makes the judge so mad that he’s placed in contempt (largely because he won’t stop talking about how traffic court isn’t a legitimate court).

By the time Sheldon’s finished with the whole court debacle, Penny comes up with a genuinely insane idea: what if they just go to Lee’s house? They do, and unsurprisingly, Sheldon is so weird and off-putting to Lee that the Marvel head honcho ends up getting a restraining order against him. “The Excelsior Acquisition” features some of Sheldon’s worst behavior, but it’s also a great rewatch.

Just like the episode where Amy and Sheldon finally consummate their relationship is a big deal for “The Big Bang Theory,” the episode where the couple shares their first kiss — Season 7’s “The Locomotive Manipulation” — is also an absolutely vital one, and it remains fresh even after tons of rewatches. Trying to plan a romantic Valentine’s Day getaway, Amy books a vintage train ride to Napa Valley for her, Sheldon, Howard, and Bernadette, hoping that being aboard a train will help Sheldon feel a little bit more amorous than he normally does. Unfortunately for Amy, Sheldon is so obsessed with the train that he almost entirely ignores her, leaving her pretty miserable; meanwhile, back in Pasadena, Leonard and Penny agree to dogsit for Raj’s precious pup Cinnamon, only to accidentally let the dog eat a ton of toxic chocolate while they’re not paying attention.

As Sheldon grows closer to his new friend Eric (Eric Petersen) instead of spending quality time with Amy, Howard and Bernadette watch this disaster unfold in front of them, and Leonard and Penny get scolded by a veterinarian, “The Locomotive Manipulation” chugs along nicely, building to a point where, after Sheldon and Amy argue about a lack of romance, he stuns her into silence by kissing her. Definitely add this one to your rewatch list.

Not only is “The Bath Gift Item Hypothesis” — a Season 2 episode of “The Big Bang Theory” — a big milestone episode for Leonard and Penny, but it’s also a great episode for Penny and Sheldon. When it comes to the Leonard and Penny of it all, Leonard grows jealous when Penny starts dating a famous scientist with whom he’s working, David Underhill (Michael Trucco), but when Penny realizes David is married, she ends up seeking solace in Leonard’s comforting arms. As for Sheldon’s dilemma of the week, he starts stressing when Penny reveals that she found him a perfect Christmas gift and decides to try and exactly match the value of whatever money she spent to get her a gift in return, being practical to a fault; he tries to do this by buying a basket of bath-related gifts and plans to return whatever surpasses the value of Penny’s gift.

Unfortunately and fortunately for Sheldon, Penny’s gift is quite literally priceless: during a shift at the Cheesecake Factory, Leonard Nimoy happened to be eating there and she swiped a napkin that he used just for Sheldon. Absolutely overwhelmed by emotion because he now has a piece of Nimoy’s DNA, Sheldon gives Penny the entire gift basket and even hugs her, which is notable considering his aversion to physical touch. Not only is this a fully rewatchable episode, it’s great to revisit around the holidays.

The Season 1 episode “The Pancake Batter Anomaly” is on this list for one incredibly specific reason: it introduces one of the most long-standing pieces of lore found within “The Big Bang Theory.” Apparently, this early in the series, everybody except for Penny knows that whenever Sheldon gets sick, he terrorizes everybody trying to get them to take care of him; as a result, Howard, Leonard, and Raj make a run for it and leave Penny in charge of the difficult patient. This is when Penny, along with the audience, learns something vital about Sheldon — whenever he was sick as a child, his mother would sing a song called “Soft Kitty” to make him feel better.

While the boys attend a “Planet of the Apes” movie marathon to kill time until Sheldon gets better, Penny and Sheldon unexpectedly bond for the first real time in the series, while Penny grows angry at Leonard’s utter selfishness. Yes, Sheldon is a total pain in the butt in “The Pancake Batter Anomaly,” but there’s a sweetness and a vulnerability we see from him in this episode that’s new at this point in the show, so rewatch this one if you want to see the first appearance of “Soft Kitty.”

“The Big Bang Theory” tends to traffic in more cerebral humor than outright slapstick, which is probably why the Season 3 standout episode “The Precious Fragmentation” feels particularly fun to revisit. After hitting up a local garage sale instead of picking up dinner — irking a very hungry Penny back at the apartment — the guys realize that amongst their haul is what seems to be a pretty solid “replica” of the One Ring from Peter Jackson’s Oscar-winning “Lord of the Rings” film trilogy. Realizing it’s worth a ton of money, they all fight over it until Penny is given the ring for safe-keeping (making her even more annoyed as she remarks that this is the first piece of jewelry her boyfriend Leonard has ever given her, she doesn’t like it or want it, and she doesn’t even get to keep it).

The literal push-and-pull over the ring — including Sheldon trying to steal it from a sleeping Penny, who rightfully slugs him — is the main focus of “The Precious Fragmentation,” and as the situation delves into the absurd (like when Sheldon envisions himself as Andy Serkis’ ring-obsessed Gollum), Penny ends up pulling Leonard out of the competition entirely with a conspicuous bag of new purchases from Victoria’s Secret. You’ll love “The Precious Fragmentation” no matter how many times you watch it.

Anyone who’s even a little bit familiar with Sheldon Cooper knows that he strenuously avoids imbibing any substances, especially alcohol … which is what makes the Season 3 episode “The Pants Alternative” particularly funny. When Leonard reveals that Sheldon is that year’s winner of the Chancellor’s Award for Science at their shared place of employment (California Institute of Technology), Sheldon is overwhelmed with excitement before realizing that he has to give an acceptance speech; naturally, he’s terrified of public speaking (as he tells Penny and Leonard, when he had to give a speech as his high school’s 14-year-old valedictorian, he fainted).

Predictably, Penny has an unorthodox solution — Sheldon should simply get very drunk. Surprisingly, Sheldon ends up taking her dubious advice and rolls up to the Chancellor’s Award ceremony half in the bag, and the next morning, he’s horrified to discover half of his new suit is missing (specifically, the bottom part). As Penny and Leonard show him on YouTube, he got so drunk he mooned the audience — which is a pretty hilarious conclusion and makes this episode super rewatchable.

To put it bluntly, Howard Wolowitz is not always the best partner to his wife and the mother of his children, Bernadette Rostenkowski-Wolowitz … but in the Season 7 episode “The Romance Resonance,” he does something so sweet that nearly all of his past transgressions could be forgiven. (Almost.) As Howard prepares to celebrate the anniversary of his very first date with Bernadette, he tells the whole gang he’s written a song for her (Howard, like Simon Helberg, has significant musical talent). Unfortunately for literally everyone but especially Bernadette, an experiment in her microbiology lab goes wrong and she’s stuck, quarantined, in the lab. Undaunted, Howard and the whole gang shows up at a window into the lab and performs Howard’s sweet ditty “If I Didn’t Have You,” which includes lines like “If I didn’t have you, life would be blue / I’d be ‘Doctor Who’ without the Tardis / I’d be a candle without a wick / A Watson without a Crick.”

Elsewhere, Penny tries to surprise Leonard with a romantic gesture of her own, so love is definitely in the air in this episode … but it’s definitely worth rewatching for Howard’s song alone. Plus, not for nothing, the song — written by Kate Micucci, who occasionally appears on the show as Raj’s girlfriend Lucy — is catchy as hell.

Remember when we said Sheldon and Penny’s friendship is the backbone of “The Big Bang Theory?” The Season 9 episode “The Celebration Experimentation” completely proves that. Against literally everyone else’s advice, Amy decides to throw a surprise birthday party for Sheldon, who’s about to turn 36; unbeknownst to her, Sheldon was once humiliated as a child when his sister tricked him into thinking “Batman” performer Adam West was coming to his party and has had an aversion to birthday parties ever since. When Sheldon shows up at the party — attended by everyone from the regular gang to Sheldon’s nemesis Wil Wheaton, playing himself, and West, who calls Sheldon “Sherman” — he flees into the bathroom, overwhelmed with anxiety. 

Leonard and Amy both insist they’ll go calm Sheldon down, but Penny is the only one who can truly coax Sheldon back out to celebrate. After going into the bathroom and quietly sitting with him, Penny admits that she would have bullied Sheldon in high school and doesn’t feel great about that. “My point is, there was a time I never would’ve been friends with someone like you, and now… you are one of my favorite people,” she says. “So, if what you need is to spend your birthday in a bathroom, I’m happy to do it with you.” Sheldon does rejoin the party, but it’s because of Penny’s friendship, and the scene between them makes this episode a really great rewatch.

There are a few weddings on “The Big Bang Theory” — Howard and Bernadette wed in the Season 6 finale, and across Season 9 and Season 10, Penny and Leonard actually get married twice — but Sheldon and Amy’s nuptials are definitely the most special when we get to see them in the Season 11 episode “The Bow Tie Asymmetry.” As everyone around Sheldon and Amy gets them ready for their big day — including Laurie Metcalf as Sheldon’s religious mom Mary Cooper, Jerry O’Connell as his brother George Jr., Courtney Henggeler as his newly pregnant sister Missy, and Kathy Bates and Teller as Mr. and Mrs. Fowler — Sheldon, always prone to distraction, has a sudden realization about his and Amy’s joint work in super-asymmetry, which ultimately wins them the Nobel Prize in Physics in the show’s series finale.

Naturally, Amy and Sheldon basically blow off their own wedding to work on the theory, leaving their officiant Mark Hamill (playing an aggrieved version of himself) to get accosted by guests curious about “Star Wars” while everyone waits for them to arrive. Sheldon and Amy’s wedding ultimately happens and is genuinely very sweet, but it’s extremely on-brand to watch these two brilliant scientists get sidetracked by their work on their own wedding day … and it makes for one of the most rewatchable episodes of “The Big Bang Theory.”

“The Big Bang Theory” is streaming on Max now.