The novel's fifteen-year-old protagonist and narrator who writes intimate letters to an anonymous "friend" to cope with his anxiety and past trauma. An introverted and observant high school freshman, he is a "wallflower" who watches life from the sidelines until he is befriended by a group of seniors.

Charlie's best friend from middle school who committed suicide the previous spring. His death is a major source of Charlie's depression and confusion at the start of the novel.

Charlie's deceased favorite aunt who died in a car accident on his seventh birthday. She appears frequently in Charlie's memories as a loving figure who lived with the family during a troubled time in her life.

A high school senior who is very pretty, popular, and often mean to boys, though she gets straight A's. She is currently in a tumultuous relationship with a boyfriend who mistreats her, a situation she keeps secret from their parents.

Charlie's older brother who has left home to play football for Penn State University. He is a source of pride for the family, and Charlie often watches his games on television with his parents.

Charlie's advanced English teacher who recognizes Charlie's intelligence and literary talent early in the year. He becomes a mentor figure, assigning Charlie extra books to read and essays to write, often inviting him to discuss literature outside of class.

A charismatic and friendly high school senior who becomes one of Charlie's first and closest friends. He is Sam’s stepbrother and is openly gay at school, though he maintains a secret relationship with the school's quarterback.

A kind, non-judgmental, and spirited high school senior who is Patrick's stepsister and quickly becomes the object of Charlie's affection. She has a reputation for being experienced and wild from her younger years but treats Charlie with genuine care and warmth.

The popular quarterback of the high school football team. He attempts to maintain a "cool" public image while hiding his secret romantic relationship with Patrick from the school and his father.

A friend of the group who attends community college and supplies marijuana to the high schoolers. He is known for his trivia knowledge and his laid-back, philosophical attitude toward life.

A strong-willed, opinionated senior in Patrick and Sam's friend group who is a devout Buddhist and feminist. She runs the school's Punk Rocky fanzine and often dominates conversations with her strong political and cultural views.

A handsome model and football player who is a few years older than the main group. He is Sam’s boyfriend for much of the book, though he often seems distracted or indifferent toward her.