With a staggering 279 episodes over 12 seasons, The Big Bang Theory is one of the longest-running sitcoms in television history. Despite receiving mixed reviews throughout most of its run, the show achieved high ratings and cultivated a loyal fanbase that remains active to this day, thanks to the spin-off show Young Sheldon.
With so many episodes to watch, there's bound to be some that register more than others. However, there are those that almost every fan has seen, the ones that remain popular and come to mind every time someone mentions the show. Whether it's because they're simply too hilarious or have meaningful moments for the characters, these episodes are required viewing for every Big Bang fan.
Pilot
The very first episode of the show, "Pilot" sees Penny moving into the apartment across from Leonard and Sheldon's. A friendship is quickly formed, mainly out of Leonard's immediate infatuation with the aspiring actress. He volunteers to go retrieve her television from her ex-boyfriend, a tall bully named Kurt, who refuses to return the TV and even de-pants both Leonard and Sheldon.
The Pilot introduces all the basic elements of the show, including all five main characters and the trademark "science talk." It also establishes the main dynamic that most storylines follow for the first three seasons, until the arrival of Amy and Bernadette.
The Bakersfield Expedition
The thirteenth episode of season 6, "The Bakersfield Expedition" features the guys going to Bakersfield Comic-Con. They, however, make an unscheduled stop at Vasquez Rocks, where Star Trek: The Original Series was filmed, to take a couple of pictures. After they're robbed, they're left stranded in the middle of the desert, in full Star Trek: The Next Generation costumes.
The most memorable part of the episode, though, is perhaps the girls' storyline. They start reading a Thor comic book and get into a heated argument concerning the God of Thunder's hammer, Mjolnir. The three deliver one hilarious line after the other, and at one point Penny compares the hammer to Harry Potter's wand.
The Parking Spot Escalation
Once Howard returns from his trip to space, the university begins to grant him special treatment. After he buys a new car, he's given Sheldon's parking space, much to the dismay of the physicist. Sheldon then steals Howard's Iron Man helmet, which leads to Howard sitting naked in Sheldon's spot.
The feud eventually escalates and drags Amy and Bernadette into the conflict, with the two trading two of the harshest burns in Big Bang history. Things get out of hand when Amy tries to hit Bernadette, in retaliation for the latter having the former's car tolled, and instead hits Penny, sending her to the emergency room. In the end, Sheldon agrees to let Howard use his parking spot, until the day he decides to buy a car.
The Opening Night Excitation
In true Big Bang fashion, the show manages to successfully combine two major events for the characters: the premiere of Star Wars: The Force Awakens and the first time Sheldon and Amy have sex. The episode even opens with a Star Wars-like opening credit crawl and features the return of Bob Newhart's Professor Proton, who appears to Sheldon in Jedi Master form.
The episode is full of landmarks, like Wil Wheaton attending the Star Wars premiere in full Star Trek costume, and Penny breaking her wine glass after Sheldon expresses his interest in being physical with Amy. In the end, all the characters get what they wanted, except perhaps Arthur, who wanted to know more about Sheldon and Amy's first time and is instead given Sheldon's reaction to The Force Awakens.
The Prom Equivalency
By season eight, every major character is in a meaningful relationship. Leonard with Penny, Sheldon with Amy, Howard with Bernadette, and Raj with Emily. Even Stuart enters into a complicated relationship with Howard's mother, much to Howard's chagrin. The couples decide to have a prom on the building's rooftop, and each attends with their significant other.
"The Prom Equivalency" is one of the sweetest episodes for Leonard and Penny and the perfect reminder of why they're so good together. Sheldon and Amy take a major step in their relationship and say "I love you" to each other. Raj and Emily prove they truly are great together, but Howard gets the short end of the stick when the cousin with whom he lost his virginity to attends as Stuart's date, making him even more jealous.
The Scavenger Vortex
Raj is known for really trying to create experiences. When he hosts a murder mystery party that none of his friends attends, he decides to mix things up and do a scavenger hunt instead. The gang divides and the episode features some of the most surprisingly effective pairs; Howard and Amy, and Leonard and Bernadette.
The first two are brought together by their mutual love of Neil Diamond and abandon the contest to go sing at The Cheesecake Factory. The other pair, led by Bernadette's killer and competitive instincts, fights Penny and Sheldon for the win, only to discover that Raj gave prizes to everyone to make all of them winners.
The Love Car Displacement
Penny accompanies the others on a road trip to Big Sur, where they'll be participating in a science conference. After a wildly uncomfortable car ride, they arrive at the hotel, where Howard gets intimidated by Bernadette's ex-boyfriend. This leads to a chaotic night where everyone switches rooms and no one gets what they want.
"The Love Car Displacement" features one of Big Bang's most hilarious scenes, in which everyone gets into an argument during the conference. They each discuss the events of the previous night in increasingly shameless and hilarious ways and the whole thing ends with Penny leaving the symposium with Bernadette's ex-boyfriend, to Leonard's horror.
The Pants Alternative
The episode that won Jim Parsons his first Emmy Award, "The Pants Alternative" is definitely a showcase for Parsons' physical comedy. Sheldon wins a prestigious science award and his friends gather to help him overcome his fear of public speaking.
When the time comes, Sheldon, unable to cope, gets drunk and descends into a meltdown while on stage. He makes insensitive jokes, sings The Elements Song, and removes his own pants, before doing the same with his underwear. To Sheldon's horror, the whole thing is caught on video and uploaded to the internet, making him go viral.
The Hawking Excitation
The first of what would be many guest appearances by the iconic Steven Hawking, "The Hawking Excitation" features Sheldon performing numerous tasks for Howard to get a meeting with the renowned scientist, whom Howard is working with.
Some of the many chores that Sheldon performs are polishing Howard's belt-buckles, going dress-shopping with Mrs. Wolowitz, and wearing a French maid outfit Howard initially bought for Bernadette. In the end, Sheldon gets to meet and even show a paper he just wrote to Hawking, only to discover he made an arithmetic mistake and the entire paper is wrong. Embarrassed, he faints and an unimpressed Hawking merely says "Great, another fainter."
The Bath Item Gift Hypothesis
When Penny says she has a gift for Sheldon, the physicist is both puzzled and troubled. He despises gift-giving but is now forced to reciprocate Penny's detail with one of his own. He enlists Howard and Raj to help him and buys numerous baskets filled with bath items so that he'll have a wide variety of options.
Penny's gift for him is a napkin both used and signed by Leonard Nimoy. Shocked that he now possesses Nimoy's DNA, Sheldon gifts her all the baskets but still claims it's not enough. He then hugs her and Leonard declares it's a Saturnalia miracle. The best Christmas episode in the show by far, the final minutes rank as one of the most joyous and wholesome moments in sitcom history.