The film was directed by Amy Heckerling and chronicles a school year in the lives of freshmen Stacy Hamilton (Jennifer Jason Leigh) and Mark Ratner (Brian Backer) and their respective older friends Linda Barrett (Phoebe Cates) and Mike Damone (Robert Romanus), both of whom believe themselves wiser in the ways of romance than their younger counterparts. The ensemble cast of characters form two subplots with Jeff Spicoli (Sean Penn), a perpetually stoned surfer, facing off against uptight history teacher Mr. Hand (Ray Walston), and Stacy's brother, Brad (Judge Reinhold), a senior who obsesses about paying off his car and easing out of his relationship with his girlfriend.

In addition to Penn, Reinhold, Cates and Leigh, this movie marks early appearances by several actors who also became stars, including Eric Stoltz, Nicolas Cage, Anthony Edwards and Forest Whitaker. Three of the actors who appeared in the film – Cage, Penn, and Whitaker – won the Academy Award for Best Actor later in their careers, with Penn winning twice.

Crowe later became a celebrated Hollywood director and screenwriter, winning an Academy Award for Best Original Screenplay for his movie Almost Famous.

The film follows the lives of several students at the fictional Ridgemont High School over the course of one academic year.

Brad Hamilton (Judge Reinhold) is a senior who appears to have it made. He is looking forward to summer vacation and almost has his car paid off. He is popular, in large part because of his part-time job at a burger joint where his girlfriend, Lisa (Amanda Wyss), also works. Brad is obsessing about how to end his long-time relationship with Lisa so he can play the field during his senior year. However, he is fired from the burger joint for insulting a customer, and when he tries to tell Lisa how much he needs her at a school rally before a big football game, Lisa tells Brad that she is dumping him to see other guys. Brad quits his next job because of the humiliation of having to wear a pirate costume when delivering food. He gets a third job at a convenience store, where he successfully thwarts an attempted robbery and is promoted to store manager.

Brad's younger sister Stacy (Jennifer Jason Leigh), who is 15, is worried that she's not attractive or experienced enough to meet let alone keep any guys. While working at the mall she meets a 26-year-old stereo salesman who asks her out (after she tells him she's 19). She sneaks out to meet him and they have sex at a local make-out place. She reveals the loss of her virginity to Linda who assures her that it will hurt less as she does it more. Damone (Robert Romanus), who earns money scalping tickets and fancies himself a suave ladies' man, lets his younger best friend Mark "Rat" Ratner (Brian Backer) in on his secrets for picking up girls. When he sees that Rat has a big crush on Stacy, he convinces him to ask Stacy out on a date. Stacy invites Rat into her bedroom after the date, but he quickly leaves when Stacy tries to initiate sex with him. Later Damone takes Stacy home after school and asks to come into her house. Damone has a premature ejaculation when having sex with Stacy and then flees in embarrassment. When Stacy tells Damone she is pregnant, he first agrees to pay half the fee for an abortion and to drive her to the abortion clinic, but reneges when he is unable to come up with the money. Desperate, Stacy tells Brad she needs a ride to go bowling with her friends. Brad suspects Stacy is lying and he sees her go into the clinic. Brad waits for Stacy to come out and she makes him promise not to tell their parents. Stacy tells her friend Linda (Phoebe Cates) how Damone blew her off. Linda flies into a rage and spray paints obscenities on Damone's car and school locker. At the end of the film, the viewer is informed that Stacy and Rat are having a passionate love affair, but have still not "gone all the way" while Damone gets busted for scalping Ozzy Osbourne tickets and ends up working at 7-Eleven (something he vowed he'd never let happen).

Jeff Spicoli (Sean Penn) is a surfer and habitual marijuana user in Stacy's American history class. The strict teacher, Mr. Hand (Ray Walston), has no patience with Spicoli's carefree attitude and especially not with Spicoli's wasting of class time. Finally, on the evening of the prom, Mr. Hand shows up at Spicoli's house and informs him that since he has wasted eight hours of class time over the past year, Mr. Hand intends to make up for that time now. They proceed to have a one-on-one tutoring session that lasts until Mr. Hand is satisfied that Spicoli has understood the lesson. Outside of class, Spicoli wrecks a car belonging to Ridgemont's star football player Charles Jefferson (Forrest Whitaker). To avoid being beaten up, Spicoli puts the car in Ridgemont's front lawn and paints the car with slurs supposedly written by Ridgemont's rival high school, Lincoln. An epilogue reveals that Spicoli saves Brooke Shields from drowning and then blows the reward money hiring Van Halen to play at his birthday party. Mr. Hand is left to believe everyone is on dope.

The soundtrack album, Fast Times at Ridgemont High: Music from the Motion Picture, peaked at #54 on the Billboard album chart. The soundtrack contains many quintessential 1980s rock artists.

Several of the movie's songs were released as singles, including Jackson Browne's "Somebody's Baby", which reached #7 on the Billboard Hot 100 singles chart. Other singles were the title track by Sammy Hagar, "So Much in Love" by Timothy B. Schmit and "Waffle Stomp" by Joe Walsh. In addition to Schmit and Walsh, the album features solo tracks by two other members of the Eagles, Don Henley and Don Felder. The soundtrack also included "I Don't Know (Spicoli's Theme)" by Jimmy Buffett.

Five tracks in the film, but not included on the soundtrack are: "Moving in Stereo" by The Cars, "American Girl" by Tom Petty and the Heartbreakers, "We Got The Beat" by The Go Go's, Led Zeppelin's "Kashmir," and "Jingle Bell Rock" by Bobby Helms. In addition, the live band at the prom dance during the end of the film played two songs also not on the soundtrack: "Life in the Fast Lane" by the Eagles and "Wooly Bully" by Sam the Sham & the Pharaohs.