Angela Chase, played by Claire Danes, is a 15-year-old sophomore at Liberty High.
"It just seems like, you agree to have a certain personality or something. For no reason. Just to make things easier for everyone. But when you think about it, I mean, how do you know it's even you?"

Like most teens in throes of self evaluation, Angela is attempting to discover and assert her identity. To do this, she distances herself from her past, pulling away from her parents, Patty and Graham, and her childhood friends Sharon Cherski and Brian Krakow. In their place, she befriends Rayanne Graff and Rickie Vasquez.

"So when Rayanne Graff told me my hair was holding me back, I had to listen. 'Cause she wasn't just talking about my hair. She was talking about my life."

Angela has a crush on Jordan Catalano and admires him from afar until they begin dating. They eventually break up, but remain friends.

Patty Chase, played by Bess Armstrong, is Angela's mother. Unlike among many TV couples, she is the main bread-winner and, at the beginning of the series, even employs her husband. She is opinionated and often can't help but express her strongly held beliefs, which at one point led to a confrontations with the free-spirited mother of Rayanne.

Graham Chase, played by Tom Irwin, played Angela's father. Graham is a more mother-like affectionate parent who cooks and is far less strict than his wife. He's relatively soft-spoken and continues to struggle with his role in the household and the direction of his life in general. In an effort to broaden his horizons, he decides to take a cooking class, which sparks a friendship with a female classmate, causing tension with Patty.

Danielle Chase, played by Lisa Wilhoit, is Angela's younger sister. There is an emphasis on how much she is ignored by her family. She has a crush on Brian and yearns to be more like Angela, whose life and friends fascinate her. Her voice-over narrates the penultimate episode, 'Weekend'.

Rayanne Graff, played by A.J. Langer, is Angela's new best friend at the beginning of the series. She is wild, unpredictable, sexually active, and irresponsible. However, Rayanne's freedom comes along with a negligent single mother (radiographer, tarot enthusiast, and hedonist Amber, played by Patti D'Arbanville-Quinn) and teenage alcoholism.

Enrique "Rickie" Vasquez, played by Wilson Cruz, is Rayanne Graff's other best friend. He is a gay Hispanic 15-year-old boy raised by his uncle, who physically abuses him. In 1994, Rickie is as openly gay as a teenager could be in his circumstances. When his uncle kicks him out of the house, he is fostered by English teacher Richard Katimski (who is also gay and becomes a mentor to Rickie) and his partner.

Sharon Cherski, played by Devon Odessa, was Angela's best friend throughout childhood, until Angela became friends with Rayanne. Their mothers are best friends. From Angela's point of view, Sharon represents a suffocating world of boredom and conventions as opposed to the wild world of Rayanne Graff. She is very conventional and academically-minded, as well as active in school activities, including the yearbook committee. During the series, she becomes sexually active with her football-player boyfriend Kyle and develops a grudging friendship with Rayanne by the last episode.

Brian Krakow, played by Devon Gummersall, is the geek of the show. He is remarkably intelligent and conformist. Despite his high IQ, he lacks emotional intelligence and is often socially awkward and self-righteous. This, more than anything else alienates him from his peers. Much like Sharon, he is often mistakenly believed by other characters to be devoid of emotion. He is in love with Angela, but he has no hope of her noticing him as he knows he is unattractive. Brian has known Angela and Sharon since they were all very young. He is the outsider of the show, but makes friends with Rickie towards the end of the series. The other characters usually turn to him only when they have an academic or technological query. His voice-over narrates the episode 'Life of Brian', in which we learn more about his inner and outer worlds.

Jordan Catalano, played by Jared Leto, is one of the best remembered characters of the show, though he was possibly the least seen and had the fewest lines of dialogue. He is a good-looking boy but also a major slacker who constantly cuts classes and stands on the brink of being expelled. He's nearly illiterate and is mistakenly believed to be stupid because of this. Angela is in love with him and during the series they begin an on-off relationship. Although he appears to belong to a group of rebellious teens, he is tired of the meaningless acts of vandalism that his friends commit for fun, yet he has no reason to believe that his life will change. He reveals his emotional depth in his songwriting ability and occasional - seemingly accidental - profound thoughts.

Tino was an oft-mentioned character who was never actually seen. He was allegedly a friend of Jordan and an "acquaintance" of Rayanne. Over the course of the show, each of the main teenage characters referenced Tino at least once and at least one party was attributed to him. For instance, Tino was the lead singer of Jordan Catalano's band, "The Frozen Embryos" [Later "Residue"].