Advances in neonatal care now permit the survival of very immature infants. Although candidiasis is not a new disease, the spectrum of clinical disease has greatly widened and the rate of invasive disease has increased significantly. This article reviews the history, microbiology, and epidemiology of candidal infections, both superficial and invasive. Particular attention is paid to the pathogenesis of and risk factors associated with the development of invasive disease, as well as its clinical manifestations, diagnosis, and treatment.