Parts Work is an active, reflective approach that draws on the ideas of Creative Systems Theory, a comprehensive theory of purpose, change, and interrelationship in human systems. Besides making a major contribution to the evolution of psychology and psychotherapy, it provides a direct route to the greater maturity of thought and action our times are increasingly demanding of us. Parts Work engages the various aspects of our human complexity like characters in a play. In just how it does, it helps us access and apply the whole of ourselves as systems with a depth and nuance that has not before been an option. The method provides the most reliable approach currently available for realizing the cognitive "growing up" that Creative Systems Theory calls Cultural Maturity.