The placenta plays crucial roles in the development of the fetus. Through connection to maternal circulation, the placenta allows the provision of oxygen and nutrients to the fetus while removing carbon dioxide and metabolic wastes. The placenta also provides essential hormones in pregnancy and enables immunological protection for the fetus against infection and rejection by the maternal immune system. In this chapter, pathology of abortions, as well as gestational trophoblastic diseases are discussed. Gestational trophoblastic disease encompasses a family of aggressive neoplasms, nonneoplastic lesions, and lesions with malignant potential that arise from various types of placental trophoblasts and may pose challenging diagnostic problems in daily pathology practices. Molecular genetic analysis is increasingly applied in diagnosis and predicting clinical outcome of gestational trophoblastic diseases. Recent updates on standardized reporting datasets for uterine gestational trophoblastic neoplasia, prognosis score, and tumor stage are also highlighted.