The Hitler Diaries (German: Hitler-Tagebcher) were a series of sixty volumes of journals purportedly written by Adolf Hitler, but in fact forged by Konrad Kujau between 1981 and 1983. The diaries were purchased in 1983 for 9.3 million Deutsche Marks (£2.33 million or US$3.7 million) by the West German news magazine Stern, which sold serialisation rights to several news organisations. One was the British newspaper The Sunday Times, whose independent director, the historian Hugh Trevor-Roper, pronounced them genuine; Trevor-Roper and several other academics were misled by Stern journalists who had misinformed them about the extent of chemical testing done on the documents, as well as its East German source, in an effort to conceal the discovery from other publications. Eventually, at a press conference to announce the publication, Trevor-Roper announced that on reflection he had changed his mind, and other historians also raised questions concerning their validity. Rigorous forensic analysis, which had not been performed previously, quickly confirmed that the diaries were fakes.

Kujau, born and raised in East Germany, had a history of petty crime and deception. In the mid-1970s, he began selling Nazi memorabilia which he had smuggled from the East, but found he could raise the prices by forging additional authentication details to link ordinary souvenirs to the Nazi leadership. Kujau began forging paintings by Hitler and an increasing number of notes, poems and letters, until he produced his first diary in the mid- to-late 1970s. The West German journalist with Stern who "discovered" the diaries and was involved in their purchase was Gerd Heidemann, who had an obsession with the Nazi era. When Stern started buying the diaries, Heidemann stole a significant proportion of the money.

Kujau and Heidemann spent time in prison for their parts in the fraud, and several newspaper editors lost their jobs. The story of the scandal was the basis for the films Selling Hitler (1991) for the British channel ITV and the German cinema release Schtonk! (1992).

Stern (pronounced [ʃtɛʁn], German for "Star") is an illustrated, broadly left-liberal, weekly current affairs magazine published in Hamburg, Germany, by Gruner + Jahr, a subsidiary of Bertelsmann. Under the editorship (1948–1980) of its founder Henri Nannen, it attained a circulation of between 1.5 and 1.8 million, the largest in Europe's for a magazine of its kind.Unusually for a popular magazine in post-war West Germany, and most notably in the contributions to 1975 of Sebastian Haffner, Stern investigated the origin and nature of the preceding tragedies of German history. In 1983, however, its credibility was seriously damaged by its purchase and syndication of the forged Hitler Diaries. A sharp drop in sales anticipated the general fall in newsprint readership in the new century. By 2019, circulation had fallen under half a million.