This book summarizes the current understanding of fetal Leydig cells, adult Leydig cell formation and function, hormonal and paracrine regulation of adult Leydig cell function, Leydig cell aging, the causes, consequences, and treatment of reductions in testosterone, and how new technologies might be used for both greater understanding of Leydig cell function and for treatments related to aging- and/or lifestyle-related alterations in Leydig cell function. Chapters are divided into three sections, each focusing on a key aspect of Leydig cell function. These sections are: Leydig Cells from Fetus through Aging, Leydig Cells Steroidogenesis Regulation and Mechanisms, and Leydig Cell Function in Health and Pathophysiology. Written by experts in the field, this book provides a comprehensive approach to the hormone production, function, and pathophysiology of Leydig cells from the fetal to adult stage of development. Leydig Cells: Formation, Regulation and Function in Health and Pathophysiology will be of particular interest to those involved with men?s health and disease, including reproductive medicine, endocrinology, urology, oncology and prenatal and postnatal development of male reproductive function.