About the book (from Wikipedia):
The Goebbels Diaries are a collection of writings by Joseph Goebbels, a leading member of the German Nazi Party (NSDAP) and the Reich Minister of Public Enlightenment and Propaganda in Adolf Hitler’s government from 1933 to 1945. The diaries, which have only recently been published in full in German and are available only in part in English, are a major source for the inner history of the Nazi Party and of its twelve years in power in Germany. The British historian Ian Kershaw wrote in the preface to his biography of Hitler: “For all the caution which must naturally be attached to Goebbels’s regularly reported remarks by Hitler … the immediacy as well as the frequency of the comments makes them a vitally important source of insight into Hitler’s thinking and action.”
