Sigmund Freud (1856-1939) and C.G. Jung (1875-1961) began corresponding in April 1906. The following year, they met in person for the first time in Vienna and engaged in a thirteen-hour conversation without interruption. Over the next seven years, they wrote to each other regularly, often just a few days apart. The correspondence, which consists of around 360 letters, was fully published in 1974. This edition, which has been shortened to focus on the professional aspects, aims to make the essence of their exchange—the fateful encounter of two world-famous men and the courage with which they faced the bitter hostility of the medical world of their time—accessible to a broad readership. The writings unfold the story of the relationship between these two great explorers of the human psyche step by step, although the seeds of their later conflict are already visible.