The basic requirement of successful implantation depends on the competence of developing embryo and the simultaneous coordination of endometrium that is receptive to the embryo. Accordingly, endometrial receptivity to implantation of embryo is induced with the cross talk between these two pivotal factors. This interaction is regulated by a number of immune cells and complex molecules such as hormones, cytokines, and growth factors. To date, this very intricate process has been understood with the data from both experimental and clinical fields and some application to clinical management were undergone in treatments for recurrent pregnancy loss and in vitro fertilization cycles. Further studies are necessary for comprehension of the cross talk in embryo implantation and more effective modality of treatment.