From January 1912 to May 1915, Arnold Schoenberg kept a diary—the only one of his works—in which he recorded his experiences, feelings, and reflections. Despite its brevity, it is a document of enormous interest, as it gives us a snapshot of his life in Berlin at a pivotal moment in his career, while he was composing Pierrot Lunaire. This volume also includes the text with which he presented his comic opera From Today to Tomorrow in a radio broadcast by FunkStunde Berlin. Furthermore, Josef Rufer, Schoenberg's disciple and close collaborator, offers an essay as a tribute in gratitude for what he experienced and learned from the master from 1919, when he met him, until his death.