Vasopressin is a hormone involved in water balance and osmoregulation. It is produced by the hypothalamus and released by the neuro-pituitary. In this book, the authors discuss the mechanisms of action, physiology and side effects of vasopressin. Topics include the study of the role of vasopressin in hypothalamo-pituitary-adrenocortical (HPA) axis regulation; vasopressin used in both adult and pediatric vasodilatory shock and cardiac arrest; the therapeutic potential and challenges of modulating myometrial smooth muscle tone through the vasopressin V1A receptor; the efficacy of vasoactive medications in acute variceal bleeds; and the reproductive and metabolic responses of desert adapted common spiny male mice to vasopressin treatment.