Star Wars is a vast science fiction franchise which started when film maker George Lucas released the film "Star Wars" in 1977. It is one of the highest grossing films of all time (by number of ticket sold). Since then six movies, books, cartoons and video games have been made. The guys often refer to Star Wars plots, characters and weapons. Penny, who is not as sci-fi fluent as her friends, often uses Star Wars as her first guess during games. The gang makes references to Star Trek more often than to Star Wars.
In the "Pilot", Sheldon mentions Leonard's Star Wars hair products that are in the shower which their new neighbor Penny is using.
In "The Euclid Alternative" (S02E05), Sheldon buys Star Wars bed sheets, but finds the sheets too stimulating to sleep, remarking that he is uncomfortable with Darth Vader "watching him sleep".
In "The Lizard-Spock Expansion" (S02E08), Sheldon refuses to watch the Clone Wars TV series with Leonard until he sees the the movie. Leonard protests, but Sheldon suggests they decide with a game of Rock Paper Scissors Lizard Spock, so he just gives Sheldon the remote, who then changes the channel.
In "The Maternal Capacitance" (S02E15), Raj and Howard make fun of the fact that Leonard's younger siblings are far more successful than him, comparing him to Jar Jar Binks, followed by the two mocking him with Gungan accents.
In "The Dead Hooker Juxtaposition" (S02E19), Sheldon attempts to mimic Admiral Ackbar's famous line from "Return of the Jedi"; "Ah, it's a trap!". He tells Penny to imagine him with a squid head, however Ackbar's species, the MonCalamari, are based on amphibious fish. Their neighbors on their home-planet Dac, the Quarren, are based on squid.
In "The Vegas Renormalization" (S02E21), Raj and Howard compare C-3PO to Sheldon, as they share many traits, however Sheldon does not believe he has any resemblance to the droid. Later, when Sheldon is trying to find his key, he hums a Star Wars theme song. Later, Penny is playing twenty questions with Sheldon, is confused and guesses "Are you Star Wars?"
In "The Monopolar Expedition" (S02E23), Sheldon references The Battle of Hoth when Han Solo cut open his deceased Tauntaun mount and used it for a heat source, saving Luke Skywalker from freezing to death. An irritated Howard suggests cutting open Sheldon and doing the same, prompting Leonard to restrain him.
In "The Electric Can Opener Fluctuation" (S03E01), Leonard claims that when Sheldon is upset, he puts on his Darth Vader helmet and tries to choke Leonard to death with the Force. Later at work, Sheldon tries to Force-Choke Raj, feeling bad for Sheldon, Raj pretends it works.
In "The Creepy Candy Coating Corollary" (S03E05), Sheldon taunts Will Wheaton by saying that his current card deck would be about as much help as an air conditioner on the ice planet Hoth.
In "The Large Hadron Collision" (S03E15), Sheldon references Anakin Skywalker's betrayal to the Jedi order, and his transformation into Darth Vader.
In "The Cruciferous Vegetable Amplification" (S04E02), Howard keeps making Star Wars droid jokes (i.e. C3PO) when Sheldon is using his Mobile Virtual Presence Device (MVPD), e.g; Howard calls Sheldon "R2-D2", and threatens to sell him to Jawas on Tatooine.
In "The Zazzy Substitution" (S04E03), Leonard refers to their group of friends as the Rebel Alliance, but Sheldon prefers the Galactic Empire.
In "The Hot Troll Deviation" (S04E04), Sheldon sarcastically states that Star Wars I: Phantom Menace is a timeless classic, implying he dislikes the first three movies, and prefers the Original Trilogy (IV-VI). Howard has two exact-replica green lightsabers above his bed, these are also seen in, The Pulled Groin Extrapolation, and The Russian Rocket Reaction.
In "The Irish Pub Formulation" (S04E06), Sheldon tells Leonard that he is to short to be Darth Vader, saying he would make a better Ewok.
In "The 21-Second Excitation" (S04E08), they note that they should go see Raiders of the Lost Ark before it gets changed like George Lucas keeps doing to the Star Wars pictures. Jar Jar Binks from Episodes 1 - 3 is also mimicked a couple of times during the episode with Wil Wheaton doing it once.
In "The Justice League Recombination" (S04E11), one of the people at the costume party is dressed as a Stormtrooper from Star Wars IV-VI.
In "The Thespian Catalyst" (S04E14), Howard refers to Darth Vader planning to construct the Death Star, however this statement is incorrect, as it was Darth Sidious who ordered the construction of the Death Star, Darth Vader simply utilized it.
In "The Herb Garden Germination" (S04E20), there is a poster in Sheldon's bathroom depicting some of the best known bounty hunters in the Star Wars Original Trilogy, including Boba Fett, Greedo, and Dengar.
In "The Russian Rocket Reaction" (S05E05), Sheldon taunts Leonard's "betrayal" by saying if he were Obi-Wan he would have said "Excuse me, Mr. Stormtrooper, these ARE the droids your looking for." Leonard argues that he is just going to Wil Wheaton's party, not turning R2-D2 & C-3PO over to The Empire.
In "The Good Guy Fluctuation" (S05E07), some Star Wars action figures are seen behind Leonard when he first talks to Alice; an ARC Trooper, & Aura Sing.
In "The Isolation Permutation" (S05E08), Sheldon is making a model of the Death Star out of LEGO.
In "The Ornithophobia Diffusion" (S05E09), Lenard rents a Star Wars movie on blu-ray, Sheldon wants to watch Star Wars but is distracted by a blue jay. When he tries to scare the bird with a broom, Sheldon puts on a Boba Fett helmet.
In "The Friendship Contraction" (S05E15), when Sheldon wakes up Leonard for the "apocalypse drill", a stormtrooper figurine can be seen on his nightstand. Leonard uses a lightsaber as a light source during a blackout.
In "The Weekend Vortex" (S05E19), the guys are playing the Star Wars online game Star Wars: The Old Republic all weekend. Amy accidently says they are playing a Star Trek game. Penny corrects her that the guys don't like them being mixed up. Amy asks what the difference is and Penny claims that there is no difference.
In "The Hawking Excitation" (S05E21), people thought Sheldon's Steven Hawking costume was R2-D2.
In "The Launch Acceleration" (S05E23), Penny parodies Darth Vader's famous line "I am your father!" When she inhales a voice-deepening gas.
In "The Date Night Variable" (S06E01), when Raj goes to the comic book store, there is a poster of C-3PO, a Chewbacca coffee mug, and a display case full of clone action figures.
In "The Cooper/Kripke Inversion" (S06E14), Sheldon plays the Imperial March, calling it his "I am unhappy and want to destroy the planet" song. He also wears an afghan blanket over his head making him look like Darth Sidious.
In "The Hesitation Ramification" (S07E12), after Penny's scene on "NCIS" is cut from her episode, Leonard finds an internet audition offer for the new Star Wars movies. Unfortunately it's for fans and not a professional audition. To make her feel better he uses a Star Wars analogy (Luke Skywalker having only one chance to destroy the Death Star), however Penny doesn't really want it. Part of Howard's Star Wars audition taping session is also shown.
In "The Occupation Recalibration" (S07E13), When Bernadette visits Stuart, there are action figures of Darth Maul, Darth Vader on display, and two models of Darth Sidious on his throne. When Bernadette and Stuart go to the other comic book store there is a display of several Star Wars characters; Darth Malgus, Darth Maul, Asajj Ventress, Captain Rex, Stormtrooper, Chewbacca, Shaak Ti and a life-size statue of C-3PO. Penny tricks Sheldon into doing yoga by making him think she said "Yoda". When Bernadette returns to Jesse's comic book store an Imperial Guard statuette can be seen on the shelf, and a Yoda figurine is standing on the cash register.
In "The Convention Conundrum" (S07E14), Sheldon goes to ask James Earl Jones to appear in his own Comic-Con. He ends up having an amazing evening with Jones, and even gets to pull a prank on Carrie Fisher.