In Janus: A Summing Up, Arthur Koestler successfully distills the past three decades of his writings on mind, paranormal experience, biology, psychology, and creativity. Because Koestler, now well into his seventies, is a Renaissance man-novelist, political journalist, philosopher, and in Janus an essayist bent on correlating a humanistic view of man with the empirical data of the life and physical sciences-Janus is able to contain coherently many diverse worlds. Moreover, Koestler incorporates these diverse materials within a General Systems Theory that encompasses all phenomena. This theory posits open systems of hierarchical levels of organization, rather like a branching tree which at each level allows a certain degree of autonomy, or wholeness, even while each level is constrained by being part of a greater whole. Koestler's metasystem thus provides the reader with a rare vision of the possible interconnectedness not only among the sciences, but also between the two cultures.