Kelly Brownell, who directs Yale's Rudd Center for Food Policy and Obesity, continues his introductory survey of how eating behavior gets shaped by biology, psychology, and public policy. This session builds on the course's opening premise that food choices are not simply matters of individual willpower, tracing how appetite, taste preference, and hunger signals interact with the food environment that surrounds most people in industrialized countries. Brownell moves between physiological mechanisms, such as how the body regulates intake, and the social and economic forces, including advertising and food availability, that push those mechanisms in particular directions. The lecture sits early in a Yale undergraduate course that later takes up obesity, eating disorders, and food policy in more detail, and this installment lays out the biological and psychological groundwork those later sessions depend on. Recorded in a Yale lecture hall as part of Open Yale Courses.