The benefits of physical exercise in the mental health are widely accepted. The neuroanatomical substrates and neuromediators that support this statement have been analyzed by several studies. However, this book focuses on the serotoninergic system activation during physical exercise, mainly because disorders in the serotoninergic neurons are involved in several mental illnesses, such as anxiety and depression. Thus, this book presents the main concepts of physical exercise and its health benefits, besides reviewing the serotoninergic system in the central nervous system. An animal experimental model is described to confirm the activation of the serotoninergic neurons during physical exercise. This book is an excellent introduction for readers to learn about the probable effects of physical exercise in the serotoninergic neurons. New studies will possibly follow this initial book in order to show that physical exercise is one of the best choices for keeping the brain away from anxiety and depression during aging.