Biochemical genetics focuses on the pathophysiology, diagnosis, and treatment of inherited metabolic disorders. While individually rare, the combined incidence of these diseases is likely greater than 1:3000 live births. These conditions may present in the neonatal period as an acute, life-threatening illness, or may manifest later in childhood with symptoms of progressive neurodegeneration, skeletal abnormalities, and/or dysmorphia. The purpose of this introductory unit is to provide an overview of the different clinical categories of metabolic disorders, modern diagnostic methods, and treatment options. © 2011 by John Wiley & Sons, Inc.