Biochemical genetics focuses on the pathophysiology, diagnosis, and treatment of inherited metabolic disorders. While individually rare, the combined incidence of these diseases makes them a significant source of morbidity and mortality, particularly among infants and young children, and new conditions continue to be identified. Inherited metabolic disorders may present as an acute, life-threatening illness or with more chronic, progressive symptoms. Population-scale newborn screening allows for early detection and treatment for < 40 different metabolic disorders. This introductory unit is intended to provide an overview of the different clinical categories of metabolic disorders, including a description of modern diagnostic methods and treatment options.