The History of Testosterone: From Antiquity to Modern Times -- Testosterone: Molecules and Receptors -- Physiology of Male Gonadotropic Axis and Disorders of Sex Development -- Utility and Limitations in Measuring Testosterone -- Male Puberty: What Is Normal and Abnormal? -- Gynecomastia -- Hypogonadotropic and Hypergonadotropic Hypogonadism -- Functional Hypogonadism -- Male Hypogonadism and Aging -- Male Hypogonadism and Traumatic Brain Injury -- Male Hypogonadism and Fertility -- Anabolic Steroid-Induced Hypogonadism -- Testosterone Therapy: Oral, Buccal and Nasal Androgens -- Testosterone Therapy: Transdermal Androgens -- Testosterone Therapy: Injectable Androgens -- Benefits and Adverse Events of Testosterone Therapy -- Testosterone and Sexual Function -- Testosterone Therapy and Prostate -- Testosterone and Cardiovascular Effects -- Testosterone and Women -- Transgender Care and Testosterone Hormone Therapy -- Testosterone and Endocrine Disruptors -- Testosterone Misuse and Abuse.