An assortment of words are used to describe infections of the fetus and newborn, including—but not limited to—“congenital,” “in utero,” “transplacental,” “ascending,” “perinatal,” and the useful but increasingly antiquated acronym “TORCH.” This chapter aims to simplify the terminology and explain the shared pathogenesis of congenital infections as well as the clinical variation between infected mothers and their infants. Why do some infections reach the fetus while others do not? Why do some infants have obvious clinical illness while others are asymptomatic? These questions and more are discussed here.