The Diary of a Young Girl is a book based on the writings from a diary written by Anne Frank while she was in hiding for two years with her family during the Nazi occupation of the Netherlands. The family was apprehended in 1944 and Anne Frank ultimately died of typhus in the Bergen-Belsen concentration camp. After the war, the diary was retrieved by Anne's father, Otto Frank.

First published under the title Het Achterhuis: Dagboekbrieven van 12 Juni 1942 – 1 Augustus 1944 (The Annex: diary notes from 12 June 1942 – 1 August 1944) by Contact Publishing in Amsterdam in 1947, it received widespread critical and popular attention on the appearance of its English language translation Anne Frank: The Diary of a Young Girl by Doubleday & Company (United States) and Vallentine Mitchell (United Kingdom) in 1952. Its popularity inspired the 1955 play The Diary of Anne Frank by the screenwriters Frances Goodrich and Albert Hackett, which they subsequently adapted for the screen for the 1959 movie version. The book is now considered one of the key texts of the twentieth century.

Anne Frank began to keep a diary on her thirteenth birthday, 12 June 1942, three weeks prior to going into hiding with her mother Edith, father Otto, sister Margot and four other people, Hermann van Pels, Auguste van Pels, Peter van Pels, and Fritz Pfeffer, in the sealed-off upper rooms of the annexe of her father's office building in Amsterdam. In her diary, the van Pels are known has the van Daans and Fritz Pfeffer is known has Mr. Dussel. With the assistance of a group of Otto Frank's trusted colleagues they remained hidden for two years and one month, until their betrayal in August 1944, which resulted in their deportation to Nazi concentration camps. Of the group of eight, only Otto Frank survived the war. Anne died in Bergen-Belsen, from a typhus infection in early March, shortly (about two weeks) before liberation by British troops in April 1945.