This chapter explains the significance of implantation in human development. It describes the development of the placenta, including the role of the decidua, chorion, and genomic imprinting. The placenta serves as respiratory, digestive, excretory, and endocrine systems for the developing embryo and fetus. A portion of the chorion and a portion of the decidua cooperate to form the placenta. The placenta arises from the intimate relationship developed between the chorion frondosum and the decidua basalis. The chapter presents the functions of the placenta and its significance in human development as the organ of cooperation between mother and unborn child. It provides the problems that can occur with the placenta, such as abruptio placentae and placenta previa. The chapter shows how the umbilical cord's anatomy allows interaction between the embryo or fetus and placenta through the process of umbilical circulation. The surface of the umbilical cord is covered by a layer of amnion, which gives it a shiny appearance.