C. G. Jung was a Swiss psychiatrist whose experimental research with the word association test provided the first independent empirical evidence supporting some of the most controversial elements of Sigmund Freud’s psychoanalytic theories. After finally meeting in 1907, Jung and Freud collaborated on the early development of psychoanalysis, with Jung eventually becoming the first president of the International Psychoanalytic Association. Differences between the two, having largely to do with their respective understanding of the dynamics of the unconscious, the relationship of depth psychology to religion, and the fundamental motivating issues in psychology, resulted in the collapse of their personal and professional relationship in 1912. Jung went on to establish his own system of depth psychology, which involved a deep exploration of mythological and religious symbolism, as well as a process of self-analysis that culminated in his positing the existence of a level of unconscious phenomena deeper than the personal unconscious studied by Freud, which he called the collective unconscious. This level of the psyche was comprised of numinous elements Jung referred to as archetypes. He also developed a complex theory of personality, coining terms such as introversion and extraversion. Later in life he turned his attention to pre-modern traditions in the West, such as alchemy, which, he argued, constituted a form of proto-psychology that anticipated aspects of his own system. In collaboration with the quantum physicist Wolfgang Pauli he investigated the occurrence of meaningful coincidences or synchronicities, thereby opening an investigation of the relationship between mind and matter that continues to this day. Jung’s influence on the practice of psychotherapy, the interpretation of literature and the arts, research in the sciences of the mind is extensive.