In this work, the endocrine and histological preparations of the uterine environment for embryo/foetus survival are covered, through compilation of relevant research results pertaining ovarian, uterine and placental changes. Also, a general overview of the ovarian cycle, uterine changes, development of the placenta, nutritional and immunological mechanisms of embryo acceptance and protection, as well as some of the most outstanding causes of embryo/foetus mortality. Each chapter involves a general discussion of relevant and pertinent research findings, including already accepted facts and those which open the possibility of new research directions. Synthesis of possible mechanisms of main biological phenomena are illustrated. More than 400 references were taken into account and herein presented, as well as photographs and illustrations.