The conditions that permit the genetically distinct fetus to survive and develop within the mother are among the most fascinating immunologic puzzles. The presence of dendritic cells in the maternal decidua pointed to a biologic role of antigen-presenting cells in maternal–fetal interaction. The method of study included recent findings on the lineage, maturity, phenotype and function of dendritic cells at the maternal–fetal interface. The increment of uterine dendritic cells occurs simultaneously with the decisive phase of gestation, when implantation takes place. Decidual dendritic cells of the first trimester pregnancy, with a phenotype characteristic of the mature myeloid lineage, express MHC class II, co-stimulatory and adhesion molecules, control Th1/Th2 balance and activate the proliferative response of autologous NK cells. Dentritic cells are specifically equipped to control immunity, to trigger immune response and also to maintain tolerance, avoiding the rejection of the conceptus by the maternal immune system.