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 (i.e., prescription drugs of abuse that are subject to stricter government regulation). Information collected by PDMPs may be used to support access to and legitimate medical use of controlled substances; identify or prevent drug abuse and diversion; facilitate the identification of prescription drug-addicted individuals and enable intervention and treatment; outline drug use and abuse trends to inform public health initiatives; or educate individuals about prescription drug use, abuse, and diversion as well as about PDMPs. How PDMPs are organized and operated varies among states. Each state determines which agency houses the PDMP; which controlled substances must be reported; which types of dispensers are required to submit data (e.g., pharmacies); how often data are collected; who may access information in the PDMP database (e.g., prescribers, dispensers, or law enforcement); the circumstances under which the information may (or must) be accessed; and what enforcement mechanisms are in place for noncompliance. States finance PDMPs using monies from a variety of sources including the state general fund, prescriber and pharmacy licensing fees, state controlled substance registration fees, health insurers' fees, direct-support organizations, state grants, and/or federal grants. The federal government has established two grant programs aimed at supporting state PDMPs: The Harold Rogers PDMP grant, administered by the Department of Justice, and the National All Schedules Prescription Electronic Reporting Act of 2005 (NASPER) grant, administered by the Department of Health and Human Services. State PDMPs vary widely with respect to whether or how information contained in the database is shared with other states. While some states do not have measures in place allowing interstate sharing of information, others have specific practices for sharing. An effort is ongoing to facilitate information sharing using prescription monitoring information exchange (PMIX) architecture. Legislation has been introduced in the 112th Congress that would take up these issues. The available evidence suggests that PDMPs are effective in reducing the time required for drug diversion investigations, changing prescribing behavior, reducing "doctor shopping," and reducing prescription drug abuse; however, research on the effectiveness of PDMPs is limited. Assessments of effectiveness may also take into consideration potential unintended consequences of PDMPs, such as limiting access to medications for legitimate use or pushing drug diversion activities over the border into a neighboring state. Experts suggest that PDMP effectiveness might be improved by increasing the timeliness, completeness, consistency, and accessibility of the data. Current policy issues that might come before Congress include the role of state PDMPs in the federal prescription drug abuse strategy and the role of the federal government in interstate datasharing and interoperability. While establishment and enhancement of PDMPs enjoy broad support, stakeholders express concerns about health care versus law enforcement uses of PDMP data (particularly with regard to protection of personally identifiable health information) and maintaining access to medication for patients with legitimate medical needs.