Book excerpt: Interdisciplinary Handbook of Perceptual Control Theory Volume II: Living in the Loop brings together the latest research, theory, and applications from W. T. Powers' Perceptual Control Theory (PCT) that proposes that the behavior of a living organism lies in the control of perceived aspects of both itself and its environment. Sections cover theory, the application of PCT to a broad range of disciplines, why perceptual control is fundamental to understanding human nature, a new way to do research on brain processes and behavior, how the role of natural selection in behavior can be demystified, how engineers can emulate human purposeful behavior in robots, and much more. Each chapter includes an author biography to set the context of their work within the development of PCT. - Presents case studies that show how PCT can be applied in different disciplines - Illustrates the Test for the Controlled Variable (TCV) and the construction of functional models as fruitful alternatives to mainstream experimental design when studying behavior - Shows how theory illuminates structure and functions in brain anatomy - Compares and contrasts PCT with other contemporary, interdisciplinary theories