This introduction presents an overview of the key concepts discussed in the subsequent chapters of this book. The book explores most important of James J. Gibson’s essays on the psychology of perception. Gibson’s numerous theoretical and empirical contributions to the understanding of how people perceive are innovative, controversial, often radical, and always profound. The book examines the creation and development of ecological optics, a discipline invented by Gibson to provide a psychologically appropriate and empirically based description of the information available in light. It deals with the analysis of environmental events and emphasizes the information for perceiving object motions and animal movements. The book discusses Gibson’s approach motivated the revision of many important concepts such as perceiving, acting, knowing, and development. For Gibson, realism was more than a philosophy; it was a demanding way of pursuing science. The book provides easy access to Gibson’s most outstanding papers and talks, including some that were unpublished.