This book provides an overview of the functions, uses and research insights of the progesterone hormone. Chapter One focuses on the effects of progesterone on B cells and antibody secretion. Chapter Two describes and summarizes the role of progesterone in targeting cell malignancy and recent treatments interfering in its proliferation. Chapter Three studies in vitro inhibition of melanoma cell growth and viability by progesterone. Chapter Four reviews the importance of both reproduction planning for production animals and the use of progesterone for estrus cycle control, describing its role, advantages and disadvantages of biodegradable and nonbiodegradable delivery devices and future trends in the field of progesterone delivery.