In person-oriented research (Magnusson, 1995) the goal is to understand individual function and development as a complex, dynamic, holistic, interacting system. This chapter seeks to affirm, and perhaps supplement, the person approach both conceptually and methodologically. Because pattern analysis figures prominently in person-oriented research, and because my charge here is to discuss some key concepts in the study of complex systems, I begin with a brief review of how patterns form and change in nature. Before proceeding, a caveat is in order: the intent here is not to broker physics or to try to “physicalize” human behavior. Instead, it is to elaborate pattern-formation principles as a foundation for understanding the patterns of behavior produced by brains and people, and how these patterns may be modified both by internal factors (intentions, values, memories, emotions, etc.) and interactions with the environment (Kelso, 1995). Clearly this builds upon, but also goes beyond, theories of self-organized pattern formation in physical and chemical systems (e.g., Haken, 1983; Nicolis & Prigogine, 1989).