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. It is thus imperative to understand the clinical manifestations, diagnostic criteria, and management of these perinatal infections. This chapter will focus on infectious diseases that are prevalent and significant among pregnant patients in the United States (US).