In the midst of national concern over illicit drug use and abuse, prescription drug abuse has been identified as the United States’ fastest growing drug problem. Nearly all prescription drugs involved in overdoses are originally prescribed by a physician (rather than, for example, being stolen from pharmacies). Thus, attention has been directed toward preventing the diversion of prescription drugs after the prescriptions are dispensed. Prescription drug monitoring programs (PDMPs) maintain statewide electronic databases of prescriptions dispensed for controlled substances. This book provides an overview of PDMPs with a focus on supporting access to legitimate medical use of controlled substances; identifying or preventing drug abuse and diversion; facilitating the identification of prescription drug-addicted individuals and enabling intervention and treatment; and outlining and educating the public on drug use and abuse trends to inform public health initiatives.