This book deals with W. B. Yeats's mystical experience and explores how mysticism is exemplified in his poetry. We cannot understand Yeats deeply without considering the mystical dimension always fundamentally at stake in his work. The book includes Yeats's interests in the mystical and mythical elements of the world's dominant cultures and, accordingly, his interpretation of history in a context that broadly negotiated with magic, the occult, theosophy, alchemy, astrology, mythology, mysticism, and religion. The book tackles Celtic culture and mysticism, highlighting Yeats's longing for the Celtic heroic age as represented by its heroes, namely, Cuchulain, Oisin, and Fergus. It also explores the influence Rosicrucianism had on his esoteric system, and discusses Yeats's automatic writing experience with his wife and his apocalyptic vision.