Although the immune and reproductive systems have been considered independent of each other, the cooperation of both systems are now known to be crucial for the initiation and maintenance of mammalian pregnancy. Nowadays cytokines and growth factors have became increasingly implicated in embryonic implantation. Endometrial functions, embryonic secretions and embryo-endometrial interactions require a continuous dialogue and synchronism between both partners (endometrium and embryo). The present review focuses on the Interleukin-1 system as an example of local regulator in embryonic implantation. Evidence demonstrating its presence and relevance on human endometrium physiology and human preimplantation embryonic development are presented. Furthermore, we described data suggesting the possible role of this cytokine in human implantation.