Worldwide, an estimated 7.9 million children are affected by congenital and inherited disorders. Some disorders are relatively common, affecting tens of thousands of newborns annually; others are rare, involving disorders that, in extreme cases, can affect less than 30 infants per year. However, this infrequency does not reduce the impact or burden on individuals and their families. Congenital defects can cause long-term disability, have a lifelong impact on health, and cost billions of dollars in care. Collection of population-based surveillance data ideally enables the discovery of etiologies for rare congenital disorders of unknown cause, allows for examining outcomes, and evaluating treatments and interventions for children with all types of congenital and inherited disorders. Many challenges are associated with performing population-based surveillance, such as difficulty in ascertaining appropriate diagnoses and frequent unavailability of necessary resources. This chapter focuses on the importance of population-based data and uses national and international surveillance systems as models for how these rare disorders can be better understood.