The placenta is unique among surgical pathology specimens in that it reflects the (patho)physiologies of two patients: the mother and the fetus. Placental examination may offer diagnostic, prognostic, and therapeutic information of clinical relevance to both neonates and their mothers. Pathological processes of relevance to future pregnancies may also be identified, facilitating preconception counseling as well as suggesting monitoring and potential intervention in subsequent gestations. In the setting of intrauterine or neonatal demise, the placenta may be the only, and often most useful, source of information regarding cause of death. The following chapter describes the clinical and pathologic features of both common placental pathologies and uncommon lesions with important clinical implications.