Context: The importance of prostaglandin (PG) signaling pathways to the maintenance of pregnancy and initiation of labor are well recognized. However, the complexity of these pathways and the mechanism(s) of their co-ordinated regulation in physiological and pathological conditions are only now being appreciated. Objectives: Here, we provide new evidence of a complete pathway for the biosynthesis and actions of PGD₂ and its metabolites within human gestational tissues. Materials and Methods: Using immunohistochemistry, northern and western blotting, we demonstrate the dynamic regulation of H-type prostaglandin D synthase (PGDS) in placenta during gestation; on the other hand, L-type PGDS and its prostaglandin products were detected in amniotic fluid with increased amounts associated with labor. Results: Placental tissues were shown to express both forms of the PGD₂ receptor identified to date, DP₁ and DP₂/CRTH₂, with a distribution consistent with the villous placenta being a major target, as well as source, of PGD₂. In vitro, placental PGD₂ production was shown to be stimulated upon inflammatory activation, while PGD₂ and its J-series metabolites exerted potent inhibitory effects on placental cytokine production. Conclusions: These findings suggest that PGDS-derived prostanoids play important physiological roles in the placenta, such as immunoregulation and feto-placental communication, while potentially having a regulatory role in the processes of parturition.