Elevation of the serum bilirubin level is a common finding during the first week of life. This can be a transient phenomenon that will resolve spontaneously or it can signify a serious or even potentially life-threatening condition. There are many causes of hyperbilirubinemia and each has its own therapeutic and prognostic implications. Independent of the cause, elevated serum bilirubin levels can be potentially toxic to the newborn infant. This chapter will review perinatal bilirubin metabolism and address assessment, etiology, toxicity, and therapy for neonatal jaundice. Finally, the diseases in which there is a primary disorder in the metabolism of bilirubin will be reviewed regarding their clinical presentation, pathophysiology, diagnosis, and treatment. For more extensive referencing, see this chapter in the third edition of this textbook .