C.G. Jung's letters to the artist and analysand Hedy Wyss, published here for the first time, are a unique testimony to Jung's vivid and sparkling spirit. Here we encounter the lively, compassionate and deeply human side of Jung's nature. He writes neither scientifically nor cautiously, but quite spontaneously out of his respective state of mind. He mentions his suffering from various physical ailments to Hedy Wyss, such as heart troubles and rheumatism. At the same time he struggles for the integrity of the analytical relationship and the veracity of love. Jung wrote his most important works during the twenty years of their correspondence, concluding with Mysterium Coniunctionis. Accordingly, in many of his letters to Hedy Wyss, hidden references to the problems he wrestled with at any given time can be found throughout these works. As a result, the content of Jung's letters required a comprehensive commentary. Alongside Jung's works, a private manuscript written by Hedy Wyss, in which, years after his death, she looked back on her encounters with "C.G." or the "Old Sage" as she liked to call him, furthered understanding of many details in the letters. These sources give us a unique insight into C.G. Jung's singular approach as a researcher and analyst.