Aion, a major work from Jung's later years, has long been a source of fascination for a wide variety of scholars and thinkers. Presented here are two substantial commentaries concerning this rich and complex text by two important figures in Jung's life and work: Barbara Hannah and Marie-Louise von Franz. This is the first volume in a series edited by Emmanuel Kennedy-Xypolitas, "Polarities in the Psyche," focusing on the broad theme of the opposites in the psyche. The next volume is "The Archetypal Symbolism of Animals." Hannah delivered these lectures at the C. G. Jung Institute in Zürich in 1957. Over the course of the lectures, she addresses each chapter of Aion, providing detail and in-depth analysis for selected passages and offering the reader suggestions for further sources and study. Well-paced and thoughtfully planned, she scans the work from beginning to end, bringing many subtle nuances to light. In a private interview with Claude Drey conducted in her home in the spring of 1965, Marie-Louise von Franz takes a close look at chapter fourteen of Aion, "The Structure and Dynamics of the Self." Published here for the first time, she offers a lively and free-flowing discussion of key sentences in the work.