This chapter recounts the principal uses of the construct of chaos in psychology; these are entwined with other nonlinear dynamical constructs, especially catastrophes and self-organization. Chaos theory and research is primarily concerned with seeing the consequences of nonlinearity accurately and finding patterns in dynamics. The growth in substantive applications of chaos in psychology is partially related to the development of methodologies that work within the constraints of psychological data. Investigations in cognitive neuroscience, psychophysics, clinical and abnormal psychology, group dynamics, and organizational behavior all utilize the chaos construct and supporting empirical research. The chapter summarizes the current state of the chaos construct in empirical research and theory in psychology. Trends in research indicate that human systems do not remain chaotic indefinitely; they eventually self-organize, and the concept of the complex adaptive system (CAS) has become more useful for describing the balance between order and disorder within a system. Chaos or turbulence is generally higher in healthy systems compared to unhealthy ones, and there seems to be an optimum level of variability for producing adaptive responses across many types of living systems. Current research in group dynamics is examining the connection between the behaviors of a CAS and how movements and autonomic and EEG responses synchronize among group members.