Mr. and Mrs. Frank and their teen-age daughters Anne and Margot, Mr. and Mrs. Van Daan and their teen-age son Peter, and Mr. Dussel all share the cramped space of the attic refuge. Other important characters are the Dutch— Elli, Miep, Mr. Kraler, and Mr. Koophuis—who risk their own lives to hide the Jews and bring them food.

In her diary, Anne reveals herself as an active, playful tomboy, who at first feels that nothing she does is right. By the conclusion of the story, she has developed maturity and confidence. Uprooted from her home and friends, Anne experiences a nightmarish ordeal, constantly facing the threat of the concentration camps and death. In this tense situation, Anne is constantly surrounded by the same adults, with whom she has frequent conflicts. She favors her father's companionship over her mother's. "Mother doesn't understand me," she protests as her mother tries to communicate with her. Jealous of frequent comparisons with her sister Margot, Anne fights to overcome sibling rivalry. Her relationship with Mrs. Van Daan fluctuates between friendly and antagonistic. An incessant talker, Anne is always at odds with Mr. Dussel, her roommate, who longs for quiet. Despite the endless personality clashes, magnified by the group's claustrophobic quarters, Anne manages to adjust to her plight.

Very much aware of the outside world, Anne listens to radio reports of the war's progress. She fears for her best friend Lies, who has been taken to a concentration camp, and for herself and her companions as the sounds of air raids and gunfire penetrate their shelter. In an effort to overcome her fears, Anne confides in her diary, which she names "Kitty" and treats as a personal friend.

Anne shows strength and courage in her writing, retaining her faith in human beings: "In spite of everything, I still believe in the goodness of man." Anne's optimism contrasts Peter Van Daan's initial pessimism. Rather quiet and bewildered by the sudden turn in his life, he spends much time locked in his own room. Anne gradually develops a romantic interest in Peter and convinces him not to succumb to pessimism but to hope for a better future. On dates limited to going from room to room, they talk, share ideas, and support each other.

Mrs. Van Daan seems to be an ordinary, doting mother at the book's beginning, but as the tension builds, she becomes panicky and neurotic. Moody and constantly complaining, she also boasts about her youth, her numerous boyfriends, and her active social life, much to the embarrassment of her son Peter. As the story develops, she begins to nag her husband and disturb the other people in hiding, fighting with Mrs. Frank over trivial matters such as whose dishes to use. Mr. Van Daan, on the other hand, remains reticent and tries to cover for his wife's shortcomings. But after desperation drives him to steal potatoes from the others, the roles are reversed, and Mrs. Van Daan tries to protect her husband.

Anne portrays her own family in more sympathetic terms. She depicts her mother as a quiet woman who attempts unsuccessfully to communicate with her. Mrs. Frank is puzzled because Anne lacks the natural affection and respect for her that Margot demonstrates. Kind and intelligent, Margot's reserved nature and obedience contrast sharply with her sister's rebelliousness. Anne's father leads the group, making the decisions, enforcing the rules, and providing encouragement.

Despite the selflessness and courage of some, such as the Dutch who feed and shelter the Jews, an underlying theme of Anne's account is man's inhumanity to man. Simply because of her religious beliefs, Anne is confined and lives in constant fear of death. Eventually, she does die, along with over six million other Jews during World War II.

The theme of imprisonment is also important. Confined to a small area for more than two years, the eight people are trapped by a hateful society. They must follow specific rules so as not to be detected by the workmen in the warehouse below: during the day, they must walk in stocking feet and cannot flush the toilet. They can never leave the building, and every unexpected phone call and every suspicious noise from below causes fear and apprehension. That Anne continues to grow mentally and emotionally under these conditions suggests the ability of the human spirit to transcend physical imprisonment.

Because the diary traces Anne's emotional growth as she exchanges childlike behavior and attitudes for a more adult outlook on life, Anne Frank is a coming-of-age story. A popular theme in literature, other examples of coming-of-age stories are J. D. Salinger's Catcher in the Rye and Mark Twain's Huckleberry Finn. Other themes include loneliness, romantic and filial love, and optimism and hope.