This correspondence testifies to the fruitful and finally tragic encounter of two extraordinary men. Both Sigmund Freud and C. G. Jung obtained from their friendship and the bitter end of it important impulses for their later work. The letters they exchanged between 1906 and 1913 reveal the complicated relations between the two friends, so different from each other but who were so intensely attracted to each other. His dialogue, apart from moving to analytical interpretation, is above all an essential document to know the origins and development of the psychoanalytic movement. To the constant coming and going of ideas and novelties about the specialty contained in these letters, news is added, sometimes very personal, and judgmental and humorous judgments about his contemporaries, both critics and followers.