The article opens with a fairly detailed overview of the research on nonlinear dynamic systems, deterministic chaos, and complexity theory—referred to collectively as complexity theory. The second part of the article is aimed at applying this research to an interesting discussion that has developed in the psychoanalytic literature regarding the fundamental nature of the self as either singular or multiple. Chaotic systems (a class of nonlinear systems) exhibit staggering variability, sensitivity, and adaptation in response to perturbation (in the form of sensitive dependence on initial conditions), while also demonstrating an enduring and distinctive coherence and continuity in their overall organization (in the form of strange attractors). As such, chaotic systems are useful in conceptualizing how relatively healthy people remain recognizable (or in character) in the midst of their variability, multiplicity, and change. By contrast, pathology of the self from the perspective of nonlinear dynamic systems is characterized by the repetitive, periodic and self-same quality of mental states.