This is the third volume in a series focusing on reproductive immunology. The book examines the molecular and cellular nature of immune signalling between mother and fetus, the role that this signalling plays in normal maintenance of pregnancy and how its aberrations may affect fetal development. These questions are considered under three major headings: the fetal major histocompatability complex, decidual effector cells, and cytokines. A detailed view of genetic phenomena affecting maternal fetal interaction at the molecular level is also presented. One of the most interesting concepts to evolve from this work is that the "molecular languages" of the hematopoietic/lymphoid and trophoblast decidua systems (and possibly the nervous system) are closely related and, in some cases, may be identical. In analysing the central problem of reproductive immunology from many different scientific points-of-view, the authors make clear that our somewhat parochial view of different biological phenomena will have to be revised and broadened as we find more evidence of universality in biological systems.