Implantation is crucial for normal pregnancy and embryo development. Synchronized interaction between the embryo and the endometrium is necessary for the embryo to reach the endometrial site of implantation and for the blastocyst to achieve its normal developmental capacity. The process of implantation is divided into three stages: apposition, adhesion, and invasion. The systems that regulate the course of these mechanisms are based on the secretion of hormones and on the synthesis of selected growth factors. Disruptions in these factor-derived signaling pathways prevent implantation and/or result in abortion, thus reducing fertility. This review presents the molecular basis of embryo implantation. This knowledge may be used in the future to evaluate the ability of potential recipients to receive embryos and to be used for embryo transfer.