The word placenta is derived from the Latin term meaning 'flat cake'. Despite the rather humble name, the placenta is an amazing organ that forms both the interface for selective delivery of nutrients from the mother to the fetus and also re-directs maternal metabolic, endocrine, cardiovascular and immune functions to promote fetal survival and growth. These two functions are fulfilled by different specialized trophoblast cell subtypes, and my laboratory has been studying how their formation and functions are regulated during placental development. Through molecular studies in cultured cells and tissues, genetic studies in mice, and comparative analysis of placentas from humans, rodents and farm animals, it is now possible to describe molecular pathways that control the development of all major trophoblast cell subtypes and structures of the placenta. The work has revealed an intricate complexity of cell-cell interactions, environmental factors, and molecular networks that control normal development.