Proliferation, migration and invasion of trophoblastic cells into the maternal endometrium are essential steps in human embryo implantation and placentation. Trophoblast invasion is normally limited in time, only during first and early second trimester of pregnancy, and in space, limited to the endometrium and the proximal third of myometrium. This process requires among other factors: the metalloproteinases (MMP) 2 and 9. Shallow trophoblast invasion is associated with pathologies including preeclampsia and fetal growth restriction whereas unlimited invasion is associated with hydatidiform moles and choriocarcinomas.In order to understand the role of decidua in this endometrial invasion by trophoblastic cells, we have developed a model of coculture of decidual and cytotrophoblastic cells in which we can evaluate the effect of each partner on the proliferative and invasive properties of the other.Surprisingly, decidual cells secrete highest levels of MMPs, and their invasive potential seems to be increased in presence of cytotrophoblast (CTB). In contrast, invasive properties of CTB are not modified by decidual cells.CTB secrete factors that favour invasion whereas decidua seems not to play a major role in regulating CTB invasion in vitro. Moreover, it is interesting to note that decidual cells could have potent invasive capacity which could explain, at least in part, endometriosis.