Annelies Marie Frank was a German-born Jewish girl who kept a diary in which she documented life in hiding under Nazi persecution during the German occupation of the Netherlands. She is a celebrated diarist who described everyday life from her family hiding place in an Amsterdam attic. One of the most-discussed Jewish victims of the Holocaust, she gained fame posthumously with the 1947 publication of The Diary of a Young Girl, in which she documents her life in hiding from 1942 to 1944 — it is one of the world's best-known books and has been the basis for several plays and films.

A diary is a written or audiovisual memorabilic record, with discrete entries arranged by date reporting on what has happened over the course of a day or other period. Diaries have traditionally been handwritten but are now also often digital. A personal diary may include a person's experiences, thoughts, and/or feelings, excluding comments on current events outside the writer's direct experience. Someone who keeps a diary is known as a diarist. Diaries undertaken for institutional purposes play a role in many aspects of human civilization, including government records, business ledgers, and military records. In British English, the word may also denote a preprinted journal format.