This chapter discusses placental angiogenesis, including information on placental neovascular formation as well as transformation of the vessels during gestation. By 4 weeks' gestation, the cytotrophoblasts proliferate and form the primary villi. The placenta structurally provides a very intimate relationship between the maternal blood and fetal blood. Once blood vessels are formed within the tertiary villi, they begin to remodel and adapt to the changing needs of the growing embryo and fetus. Placental angiogenesis is very complex and depends on an appropriate balance between pro-angiogenic and anti-angiogenic factors. Dysregulation of placental angiogenesis often leads to pregnancy-related diseases. Three common adverse pregnancy outcomes have been associated with defective placental vascularization: spontaneous abortion, intrauterine growth restriction (IUGR), sometimes referred to as small-for-gestational age (SGA), and preeclampsia (PE). Further characterization of angiogenesis in placental development will better inform clinicians and scientists about healthy and pathological pregnancies.