Perinatal infections encompass a range of viruses, parasites, and bacteria that can be transmitted during pregnancy from mother to fetus. Asymptomatic or undiagnosed maternal disease can result in significant fetal and neonatal morbidity and mortality. For this reason, it is important to understand the clinical manifestations, diagnostic criteria, and management of these perinatal infections. This chapter focuses on infectious diseases that are prevalent or of particular clinical significance among pregnant women in the United States.