Here are some cold hard facts: “The Big Bang Theory,” the CBS sitcom created by Chuck Lorre and Bill Prady, ran for 12 years, the same number of seasons, and an incredible 279 episodes. After it kicked off in 2007, the show almost floundered during its first season but was improbably saved, in a way, by the writers’ strike that took place until 2008; after that, the series was an unquestionable and undeniable success. Stars Jim Parsons, Johnny Galecki, Kaley Cuoco, Simon Helberg, Kunal Nayyar, Melissa Rauch, and Mayim Bialik — who play Sheldon Cooper, Leonard Hofstadter, Penny, Howard Wolowitz, Raj Koothrappali, Bernadette Rostenkowski-Wolowitz, and Amy Farrah Fowler, respectively — were all skyrocketed to fame and acclaim, and Parsons even took home a handful of Emmys for his leading role. With all of this context in mind, it can be hard to winnow down the “best” episodes of “The Big Bang Theory,” partly because of the sheer number and partly because, well, what makes an episode “the best?”

For this list, I’ve compiled some of the outright funniest episodes of “The Big Bang Theory,” as well as those with some of the show’s more emotional beats; even people looking for an easy-to-digest sitcom have to admit that, in order for it to stay interesting for 12 entire seasons, the characters have to evolve and grow. Now that the parameters are set, here are the 10 best episodes of “The Big Bang Theory,” ranked.

Ever wonder why Leonard, Howard, and Raj even deign to hang out with Sheldon, a notoriously stubborn, finicky guy who panics if someone so much as takes his “regular spot” on the couch? In season 3, we finally get an explanation in the episode “The Staircase Implementation,” an episode where, during a fight with Sheldon, Leonard sits down and tells Penny their friendship origin story. In the process, we also learn why the elevator in Sheldon, Leonard, and Penny’s building is seemingly permanently broken — and, unsurprisingly, it’s Leonard’s fault.

Throughout flashbacks — which feature Sheldon, Leonard, Howard, and Raj in some pretty wild getups that seem to come from the 1990s despite said flashbacks being set in 2003 — we see that Sheldon couldn’t keep a roommate on account of being incredibly annoying. (On his way out, the last guy, played by Steven Yeun, scrawls “DIE SHELDON DIE” on a wall in red paint, just to give you an idea of his mindset.) Out of desperation, Leonard, who’s new to the California Institute of Technology, agrees to live in Sheldon’s spare room and even agrees to Sheldon’s genuinely absurd “roommate agreement,” and eventually, he warms to Sheldon. Why? Well, Sheldon chases Leonard’s girlfriend Joyce Kim (Ally Maki) out of the apartment, and later, she turns out to be a North Korean spy. Between that and the fact that, while Howard and Leonard are playing with a combustible rocket, Sheldon saves their lives by tossing the rocket into the elevator shaft and shuts the door, their friendships are settled. “The Staircase Implementation” does a great job of providing backstory without overloading the audience, and the elevator explanation is … actually pretty funny.

“The Bakersfield Expedition,” which takes place partway through season 6 of “The Big Bang Theory,” is probably most famous for the boys’ storyline, where Sheldon, Leonard, Howard, and Raj end up stranded in the desert dressed in incredibly realistic “Star Trek” costumes. This happens while they’re heading to Bakersfield, California, for the city’s Comic-Con, which Sheldon says is all about comic book lore (as opposed to the bigger and more famous San Diego Comic-Con, which Sheldon claims “went all Hollywood,” and he’s not entirely wrong in that assessment). On the way to the convention, the guys get out of their car to take a photo in their elaborate costumes, at which point someone steals the car because Leonard left the key in the ignition. This, in turn, forces them to hitchhike since their clothing and cell phones were also in the car.

Still, I’d argue the real magic of “The Bakersfield Expedition” is the girls’ plotline. With the boys out of town, Penny, Amy, and Bernadette go and get brunch together — but partway through said brunch, they realize that maybe they’re all at least a little curious about why the guys love comic books so much and decide to give it a try themselves. After they cause a stir at Stuart Bloom’s (Kevin Sussman) Pasadena comic book store, which Sheldon, Leonard, Howard, and Raj typically frequent, the girls take their new treasures home and have a massive “debate” over who’s strong enough to carry Thor’s hammer Mjolnir. While this sudden interest in comic books doesn’t come back into play, it’s fun to watch Amy, Penny, and Bernadette have an adventure of their own and try to learn more about the weird guys they love in the process.

Something that’s going up to come up on this list more than once is that, in my estimation, Leonard and Penny aren’t the central relationship on “The Big Bang Theory.” The title doesn’t belong to Howard and Bernadette or Sheldon and Amy, either. No, the best relationship on “The Big Bang Theory” is not romantic — it’s Sheldon and Penny, two polar opposites who, throughout the series, become genuinely close friends.

The friendship between Sheldon and Penny builds over a lot of time — and episodes like “The Work Song Nanocluster,” where Sheldon helps Penny launch a small hair accessory business, or “The Adhesive Duck Deficiency,” where Sheldon helps Penny after she slips and falls in the shower, barely missed the cut for this list. Instead, I went with “The Bath Item Gift Hypothesis” for the eighth spot on this rundown, because not only does it prove just how well Penny understands Sheldon, but it’s also a fan favorite (and, not for nothing, Kaley Cuoco’s favorite episode of the series). In this episode, Penny gets Sheldon a Christmas gift, sending the guy into a tailspin; he sets out to buy her a gift basket full of luxury bath items so that once he figures out the financial value of her gift, he can return enough items to make the two completely even. (Sweet, right?) The best moment of the episode comes when we learn that Penny’s gift to Sheldon is a napkin used and signed by Leonard Nimoy himself, which Sheldon, obviously, loves, so she gets a giant gift basket and a hug from Sheldon, which is a pretty rare occurrence. Penny knew exactly what Sheldon would love and proved it, making this an excellent and important origin episode for her friendship with Sheldon.

Neil Armstrong once described his journey to space as “one small step for a man, one giant leap for mankind” — but Howard Wolowitz actually marrying the woman of his dreams is his own version of a giant leap. In the season 5 finale of “The Big Bang Theory,” Howard and Bernadette finally tie the knot just before he heads out on a daring space mission with NASA, and, frankly, it’s hard to tell which thing brings Howard more joy. (I’m kidding; it’s definitely Bernadette.) “The Countdown Reflection” is a cool experiment for this typically straightforward sitcom to boot, combining Howard’s space launch with memories of his nuptials, during which he and Bernadette were surrounded by friends and loved ones on the rooftop of Penny, Leonard, and Sheldon’s building. They choose this specific spot for their wedding for a few reasons. First, after waiting to get married at City Hall before Howard’s departure, the office closes while the lovebirds are still in line. This is when Raj and Leonard realize that if they hold the impromptu wedding on the roof, they can position it so that Google Maps satellites catch the ceremony as they pass over and give Howard and Bernadette a wedding photo that’s taken from space.

Throw in a subplot where Amy, Penny, Sheldon, Raj, and Leonard all get ordained to marry their friends — as well as an unexpectedly sweet ending where everyone but Howard watches his rocket launch and even Sheldon gets sort of emotional — and “The Countdown Reflection” isn’t just a welcome departure (sorry) for the structure of “The Big Bang Theory,” but it’s also one of the show’s best-ever episodes.

Sometimes, an episode of “The Big Bang Theory” doesn’t have to reinvent the wheel or contain any huge emotional revelations to be great; it can just be funny and, perhaps as a nice bonus, spawn a long-running meme. Penny, finding herself at a low point in life (she’s not booking acting roles, breaks her car key trying to use it to get into her apartment, and swallows a fly just walking up the stairs of her apartment building), is unexpectedly consoled by Sheldon, who invites her into his apartment, only for her to notice the computer game he’s playing. The game in question, the very real multiplayer hit “Age of Conan,” ends up ruining Penny’s life, if only for a short while.

Throughout “The Barbarian Simulation,” Penny gets way too into “Age of Conan,” which also screws up Sheldon’s careful routine (and sleep habits) because she starts calling him at all hours of the day and night to ask for advice on her playthrough. (When Leonard tries to intervene, he does so through the game itself, and Penny’s character chops his character’s head off.) It’s only when she’s nearly seduced by Howard’s “Age of Conan” character that Penny snaps out of her stupor, but all in all, it’s a really funny episode — and that picture of Penny, looking like a total mess with food on her face and her laptop in her lap, created a perfect meme to boot.

“The Romance Resonance,” which comes pretty early in season 7 of “The Big Bang Theory,” features one of Howard’s all-time sweetest moments and gestures … and also lets Amy and Sheldon move things forward just a little bit in their own romantic journey. Howard is excited to write a song for Bernadette celebrating the anniversary of their very first date, but when she ends up quarantined in her lab after an accident, the gang has to recalibrate. Instead of performing his song for her in a private dining room like he planned, Howard and the gang bring instruments to the window of her lab, where Howard sings a little ditty called “If I Didn’t Have You.” (Lyrics include witty bon mots like “Ever since I met you / You turned my world around. / You supported all my dreams and all my hopes. / You’re like Uranium 235 and I’m Uranium 238 / Almost inseparable isotopes.”)

Elsewhere, Amy realizes that Sheldon made a mistake in his work that actually led to a breakthrough, and even though Sheldon holds himself accountable for the fact that he feels like a “fraud,” it ends up bringing Amy and Sheldon just a little closer. As for Penny and Leonard, they try to settle on some outlandish gestures to celebrate their relationship … until Penny reveals that she keeps a box of trinkets and reminders of why she loves Leonard, cementing their affection for each other. “The Romance Resonance” presents all of the central couples in “The Big Bang Theory” on their best behavior … and for what it’s worth, Howard’s song is pretty catchy.

In season 9 of “The Big Bang Theory,” Amy decides to try and throw Sheldon a “surprise” birthday party … and when it predictably sends him into a complete panic, only one person in the central gang can actually talk him off the ledge. “The Celebration Experimentation,” which happens to be the 200th episode of “The Big Bang Theory,” opens as Amy wonders why Sheldon never wants to celebrate his birthday; as it turns out, it’s because when he celebrated his birthday with his twin sister as a child, he was frequently disappointed, culminating in a life-shattering event at his sixth birthday party where Batman didn’t show up as “promised.” Sheldon is eventually talked into having a birthday party, but when he arrives and sees that Amy invited a surprise guest in the form of Adam West (who wishes “Sherman” a happy birthday), he can’t handle it. (Wil Wheaton, Sheldon’s in-universe nemesis who plays a dark version of himself, is also present, which probably doesn’t help.)

Sheldon flees into the bathroom, and after Amy and Leonard briefly argue over which one of them will go and fetch him, Penny stops them both — and Sheldon allows her to join him. The two have a legitimately heartfelt talk sitting on the edge of the bathtub, where Penny admits that she probably would have bullied him in high school and is ashamed of that fact, saying that he’s one of her “favorite people.” She also tells Sheldon that they can spend the entire party in the bathroom if that’s what he wants. Eventually, though, Sheldon decides to rejoin the festivities, and it’s all thanks to Penny, which is why this episode is so good; while Amy is the one to throw the party and find an actual Batman to join them, Penny is the one who provides the emotional support Sheldon sorely needs.

Ask most fans of “The Big Bang Theory” about the season 9 episode “The Opening Night Excitation,” and they’ll tell you it’s “the one where Sheldon and Amy finally have sex.” While this is absolutely true, that’s not the entirety of the installment. It’s actually centered around the release of “Star Wars: Episode VII — The Force Awakens” (despite the fact that, in the years since the “Star Wars” sequel trilogy concluded, it feels almost foolish to see this level of excitement onscreen). Howard gets tickets to opening night, but there’s one problem: After a break-up, Sheldon and Amy have rekindled their relationship, and her birthday happens to be the same day that “The Force Awakens” comes out.

Thanks to a dream featuring Bob Newhart as his recurring “Big Bang Theory” character Arthur Jeffries (also known as Professor Proton), Sheldon decides to make the ultimate sacrifice and stays home with Amy for her birthday, and, yes, the two finally have what Sheldon always refers to as “coitus.” The episode’s finale, which shows Sheldon gasping in pleasure alongside Leonard, Howard, and Raj doing the same thing after “The Force Awakens,” is still one of the funniest gags the show’s ever pulled off, and all in all, it’s a phenomenal half-hour of “The Big Bang Theory.”

You can’t make a list of the best “Big Bang Theory” episodes and not include the series finale, “The Stockholm Syndrome.” In the buildup to the show’s last ever episode, Amy and Sheldon find out that they’re set to receive the Nobel Prize in physics for their work in super asymmetry, the building’s elevator finally gets fixed, and Amy gets a makeover that shakes Sheldon to his very core … and in the finale itself, the whole gang travels to Sweden for the Nobel ceremony. Unfortunately, Sheldon is being his typical petulant and difficult self; after finding out Penny is pregnant on the flight over, he tells everyone (he was afraid she was simply sick and is relieved that he won’t get a stomach bug), infuriating Leonard and Penny, and he also manages to alienate Howard and Bernadette as well. (They consider going home upon finding out one of their kids sustained a minor injury, and Sheldon is far from supportive.)

Amy angrily tells Sheldon that he hurt his friends, but when they stick around for the ceremony, they’re surprised when Sheldon uses his speech to extend genuine, heartfelt gratitude to Amy and all of his friends. In the finale’s very last moments, the whole gang gathers in what is now Leonard and Penny’s living room to eat dinner, with only one difference: Amy and Sheldon proudly wear their Nobel medals. It’s a fitting, perfect ending … Penny’s surprise pregnancy notwithstanding.

The best episode of “The Big Bang Theory” is also one that was really fun for the cast to film, and that’s not a coincidence. The fact that all of the lead actors had a blast making season 7’s “The Scavenger Vortex” shows, which makes it such a great half-hour of TV. The key to what makes “The Scavenger Vortex” work so well isn’t just that everyone involved is having such a good time, though — it’s because the show pairs up characters in different arrangements, giving the audience brand-new dynamics after seven seasons on the air.

Raj, who’s hurt after all of his friends blew off a murder mystery dinner he planned, insists that they all participate in a scavenger hunt of his design, placing them into three teams after deciding not to pair up couples and drawing names from a hat. Penny ends up with Sheldon, Amy and Howard play together, and Bernadette and Leonard make up the final duo. While we know that Penny and Sheldon have a great rapport, it’s always fun to see them get super competitive. Meanwhile, Amy and Howard end up bonding over their shared love of Neil Diamond’s body of work, singing his songs throughout their attempts to solve Raj’s puzzles (they even make a pit stop to perform some karaoke). As for Bernadette and Leonard, Leonard finds himself a bit cowed by how hyper-competitive Bernadette turns out to be. Raj doesn’t provide a prize to the eventual winners, making everybody mad — instead, he snuck gold coins into everyone’s pockets before the game started, making them “all” winners — but the lead-up to this reveal is phenomenal, making “The Scavenger Vortex” the best episode of “The Big Bang Theory.”

All of “The Big Bang Theory” is available to stream on HBO Max now.