This chapter discusses physiology of pregnancy and lactation, where pregnancy is the process whereby the life of a baby begins in the mother’s womb and progresses up to the stage when it is safe to expose the baby to the outside world. Zygote is the beginning of the baby. The zygote undergoes repeated cell division. After cell division, zygote is called the embryo. Implantation is the process by which the embryo sticks to the uterus. Estrogen and progesterone stimulate endometrial growth, vascularity, secretions and nutrient storage, thereby making the uterus a comfortable home for the embryo. Placenta is a structure in which fetal blood vessels come in close contact with blood sinuses containing maternal blood. Amenorrhea is absence of menstrual cycles. Amenorrhea is seen not only during pregnancy but also during lactation. Lactation is the process of secretion of milk. Secretion of milk is inhibited by estrogen and progesterone.