Gestational trophoblastic disease (GTD) is a group of diseases with variable morphology, etiopathogenesis and prognosis. GTD develops from trophoblasts or extravillous trophoblasts related with pregnancy. World Health Organization (WHO) classifies this tumor into benign group and malignant group. The benign group is comprised of hydatidiform mole, exaggerated placental site trophoblastic lesion and placental site nodule. The malignant group comprised of gestational choriocarcinoma and placental site trophoblastic tumor (PSTT). A detailed discussion on the hydatidiform mole, invasive hydatidiform mole, choriocarcinoma and placental site trophoblastic tumor has been provided in this chapter. Epithelioid trophoblastic tumor, exaggerated placental site reaction, placental site nodule are also discussed in this chapter. Three well-illustrated tables and 20 well-colored figures are also provided in this chapter, which are very helpful for students and readers.