A variety of investigators in recent years have proposed models of psychological systems based on the concepts of chaos, nonlinear dynamics, and self-organization. Unfortunately, psychologists in general have little understanding of these important ideas. These terms are defined, and their relationships are discussed. The value of applying these concepts to psychological systems is demonstrated by exploring their utility in areas ranging from neuroscience to clinical psychology. Some of the difficulties in using nonlinear concepts and methodologies in empirical investigations are also discussed.