Katherine Danziger Protagonist of the book. Katherine is almost 18 and a senior in high school who is getting ready for college. When she meets Michael, she falls in love with him. One of the novel's central plotlines is her decision to lose her virginity to him as well as the sexual relationship they share together.
Michael Wagner Boy who Katherine meets and with whom Katherine falls in love. He is a senior at another high school nearby. They meet at a New year's Eve Party, and their relationship developes from there. He nicknamed his penis "Ralph."
Erica Small Katherine's best friend, who provides her with emotional support owing to Erica's ability to see situations from a realistic point of view. She sees sex as a phsical act, not a romantic one, unlike Katherine.
Artie Lewin A boy who is friends with Katherine and Michael. He is not very confident about himself and questions his sexuality and wonders if he is gay. Erica breaks up with him at a party after he scared her by saying he will commit suicide, and two days later he attempts to, resulting in him not graduating from High School.
Sybil Davison Katherine's friend (and Erica's cousin) who later gets pregnant when having loveless intercourse because she wanted to have experience in giving birth. She put the baby up for adoption, and hoped that they would name her baby girl Jennifer.
Jamie Danziger Katherine's little sister. She is proficient in music, art, and cooking. She is in the seventh grade and looks a lot like Katherine. She used to say that she was jealous of Jamie, but it passed.
Roger Danziger Katherine's father, a pharmacist who owns two drug stores.
Diana Danziger (née Gross) Katherine's mother, a librarian. She gives Katherine sexual advice.
Hallie Gross Katherine's maternal grandmother, a lawyer and progressive liberal.
Ivan Gross Katherine's maternal grandfather, who had previously had a stroke (he had to walk with a cane and sometimes at a loss for words), and would have another one later in the book which would claim his life.
Theo An older boy who Katherine inadvertently falls for while working at a camp, which spells the end of her and Michael. He also started the masscre of calling her Kat, and others started calling her that, though she disliked it.
David A boy Jamie falls in love with, and started a relationship with.