Human endometrium and in particular decidua, harbours a considerable population of immunocompetent cells. The most prominent of these are uterine natural killer (uNK) cells, which differ considerably from their peripheral blood counterparts in terms of both gene expression and function. Recently, the existence of DC-SIGN positive immature dendritic cells (DCs) in human decidua has been demonstrated. Evidence exists that immature DCs are required for the initiation and maintenance of peripheral tolerance, whereas mature DCs, which are only found in minimal amounts in human decidua, are associated with a Th1 polarization of T cells. Although the study of uNK-DC cross-talk is only beginning, it may in the future provide important insights into how acceptance of the fetus by the maternal immune system is mediated.