Nonlinear dynamical systems (NDS) theory is the study of how complex processes unfold over time and is sometimes known as chaos theory or complexity theory. Perhaps it was one of those experiences in which “You had to be there,” but the early days of NDS in psychology were rife with excitement. There was so much potential for solving old and new problems and transforming the way psychology was studied that everyone present knew it could occupy entire careers. The days of saying, “Here's what chaos and complexity can do!” were gone years ago, however. NDS scholars have embarked on the less glamorous but ultimately more important task of systematic model building and developing an empirical research agenda. We estimate that about 50 books are published each year that are relevant to some aspect of NDS, psychology, and the life sciences, as well as numerous articles in peer-reviewed journals, such as Nonlinear Dynamics, Psychology, and Life Sciences, signifying that the field is moving forward at a rapid pace.

The waterfall of progress creates two dilemmas that we attempt to resolve by composing this book. The first is to answer a simple question: “What should I read first?” The second is how to reconcile the escalating gap between the state of the science in NDS and the average level of awareness of its accomplishments by professionals in psychology.

Introduction

It is rewarding to contemplate the progress in the field of nonlinear dynamical systems (NDS) science based on the work presented in this volume. Dynamical systems approaches have had a significant influence in psychology ever since its early days. Piaget used equilibrium as one of its central tenets in his description of the dynamics of child development (e.g., Piaget, 1967; see also Chapter 8, this volume); Lewin (1947) similarly analyzed the dynamical processes of information exchange in groups in terms of tendency toward equilibrium (see also Chapter 14), and gestalt psychology emphasized the unified whole in perception over its constituent perceptual elements (Wertheimer, 1925, see also Chapter 6). The chapters presented here attest to the responsiveness of psychology to the latest developments in NDS, such as chaos theory, catastrophe theory, fractal geometry, and agent-based modeling, and they illustrate the extent to which these approaches have made inroads in most of the subdisciplines in psychology, such as cognitive, developmental, clinical, and organizational psychology. In each of these areas, NDS provides novel perspectives to long-standing questions to which traditional paradigms failed to offer satisfying answers; NDS inspires scholars to ask various questions about observed phenomena and offers new, more flexible modeling strategies.