Aion: Researches into the Phenomenology of the Self is Part 2 of the Volume 9 in The Collected Works of C. G. Jung, a series of books published by Princeton University Press in the U.S. and Routledge & Kegan Paul in the U.K. Originally published in German (1951), it is a major work of Jung’s later years. Its central theme is the symbolic representation of the psychic totality through the concept of the Self, whose traditional historical equivalent is the figure of Christ.