In writing to Kitty, Frank is trying to reach out to the normal world beyond her confined quarters. She misses school and her old friends. As the youngest in the secret annex, she is treated with condescension by the adults and sometimes scolded for her boisterousness. To overcome these feelings of isolation, she invents a friend in whom she can confide.

Yet, gradually, the purpose of Frank’s writing changes. She uses her letters to give Kitty—and, by extension, the readers of The Diary of a Young Girl—a graphic description of the hardships that she is forced to endure. The book provides a gripping sense of what it was like to be in hiding, trapped in a very limited and uncomfortable space, and in constant anxiety about any unusual sound from below and about making any noise that could lead to their being discovered. Frank tells of the mounting tensions among the adults, of their quarrels, and of occasional outbreaks of hysteria, particularly on the part of Mrs. Van Daan. She voices her astonishment and disapproval of what she regards as childish behavior by the grown-ups. Although the content of The Diary of a Young Girl is often grim, the book is not by any means depressing. Frank maintains her good humor, her optimism, and her impish sense of fun despite attacks of doubt and fear. In many ways, the book is inspiring because it shows a young girl coping with adverse circumstances and upholding a positive attitude in the face of the daily horrors around her.

For a young adult audience, The Diary of a Young Girl has two main sources of interest. First, it gives an excellent insight into what occurred during World War II in the Nazi-occupied countries. Frank’s realistic account of her life illuminates the historical situation more than any secondary sources could, as her diary is an intimate and intense record of her own experiences and reactions. Readers come to know what it was like to be in her position.

Second, beyond this interest specific to its time, The Diary of a Young Girl is also of lasting importance as a document of adolescence. Despite her imprisonment in a strange environment, Frank shows all the characteristics normally associated with the difficult transition from childhood to the verge of adulthood. She rebels against her parents, especially her mother, whose well-meant but not always tactful advice she resents and rejects. She is ambivalent toward her elder sister, who has a quiet, obedient temperament quite different from her own. For a while, she is close to her father, whom she admires, but eventually she begins to grow away from him as well. Like a typical teenager, Frank spends much time and effort in the bathroom experimenting with new hairstyles and wondering whether she is attractive. The contrast between her abnormal surroundings and her very normal development is striking. Her attachment to Peter marks another stage in her adolescence; she passes many hours with him, at first finding happiness in his company but ultimately feeling disappointment at his shallowness.

The central theme of her adolescence, however, is the quest for her own identity. In the course of writing her letters to Kitty, she comes to realize that writing is her inner vocation. She dreams of growing up after the war to become a journalist and writer, although she is aware that she may not survive. In a touching passage near the end of her diary, dated April 4, 1944, she says that “I want to go on living even after my death! And therefore I am grateful to God for giving me this gift, this possibility of developing myself and of writing, of expressing all that is in me.”

Frank’s wish has been fulfilled despite her death at the age of sixteen: She has gone on living through the fame that her book has acquired. It has become a classic, widely read by young audiences throughout the world. Frank provides a memorable example of the fortitude of the human spirit in a cruel world.