In the United States, generic drugs provide ~ 90% of the prescriptions dispensed but only account for 23% of prescription drug spending. The cumulative savings due to the use of generic drugs are estimated to be as large as $1.67 trillion from 2007−2015. 1 However, the complex ecosystem that provides these generic products includes multifaceted and dynamic interaction of scientific, regulatory, and economic factors. The financial advantages for patients and consumers seem to be because of the numerous interactions of academic scientists, generic product developers, regulators, healthcare providers, and payers that comprise this ecosystem. Because of the widespread use of generic drugs, it is critical that the accuracy of decisions about generic drug substitution that this ecosystem is responsible for is supported by solid scientific foundations. In this issue, multiple articles explore the complexity of generic drug development, regulation, and use and identify key impact points for the clinical pharmacology community.The Drug Price Competition and Patent Term Restoration Act (Public Law 98-417), informally known as the Hatch-Waxman Amendments, established the approval pathway for generic drug products in the United States through the submission of abbreviated new drug applications (ANDAs). Compared with the brand name product (also referred to as the reference listed drug), a generic drug must contain the same active pharmaceutical ingredient, strength, dosage form, route of administration, and labeling and be