The coagulation and thrombotic systems of an infant are fundamentally different from those of adults and older children. Hemostatic factors have inherently lower circulation levels in infants and are also affected prenatally by conditions of pregnancy. The unique physiology of neonates can contribute to a procoagulant state, which can result in a high level of morbidity and mortality. This review outlines the epidemiology, clinical characteristics, diagnosis and management, and etiologies of congenital and acquired forms of thrombotic disorders, with a discussion of the evaluation for hypercoagulation.