Marijuana is the most commonly used illicit drug in the United States. In 2013, an estimated 19.8 million individuals in the United States aged 12 or older (7.5% of this population) were current (past month) users of marijuana. While reported marijuana use is similar to that in 2012, it has generally increased since 2007 when 5.8% of individuals aged 12 or older were current users of marijuana. The past decade has seen a decline in youth perceptions of risk tied to smoking marijuana; however, the rate of past-month marijuana use among youth declined between 2011 and 2013 (7.1%). Youth also perceive that obtaining marijuana—if they desire it—is relatively easy. Indeed, marijuana availability in the United States has increased, according to the Drug Enforcement Administration (DEA). This increase has been linked to factors such as rising marijuana production in Mexico and increasing marijuana cultivation in the United States led by criminal networks including Mexican drug trafficking organizations. The uptick in availability and use of marijuana in the United States is coupled with a general shift in public attitudes toward the substance. In 1969, 12% of the surveyed population supported legalizing marijuana; today, more than half (52%) of surveyed adults feel that marijuana should be legalized. In addition, 60% indicate that the federal government should not enforce federal laws prohibiting marijuana use in those states that allow for its use. Marijuana is currently listed as a Schedule I controlled substance under the Controlled Substances Act (CSA). This indicates that the federal government has determined that (A) The drug or other substance has a high potential for abuse. (B) The drug or other substance has no currently accepted medical use in treatment in the United States. (C) There is a lack of accepted safety for use of the drug or other substance under medical supervision. U.S. federal drug control policies—and specifically those positions relating to marijuana—continue to generate debates among policy makers, law enforcement officials, scholars, and the public. Even prior to the federal government's move in 1970 to criminalize the manufacture, distribution, dispensation, and possession of marijuana, there were significant discussions over marijuana's place in American society. While the federal government maintains marijuana's current place as a Schedule I controlled substance, states have established a range of views and policies regarding its medical and recreational use. As of November 2014, over half of all states and the District of Columbia allowed for the medical use of marijuana in some capacity. In the November 2012 elections, voters in Washington State and Colorado voted to legalize, regulate, and tax small amounts of marijuana for recreational use . In the November 2014 elections, voters in the District of Columbia, Oregon, and Alaska also passed recreational legalization initiatives. These moves have spurred a number of questions regarding their potential implications for related federal law enforcement activities and for the nation's drug policies on the whole. This report provides a background on federal marijuana policy as well as an overview of state trends with respect to marijuana decriminalization and legalization—for both medical and recreational uses. It then analyzes relevant issues for U.S. federal law enforcement as well as for the criminal organizations involved in producing, distributing, and profiting from the black market sale of marijuana. This report also outlines a number of related policy questions that Congress may confront. Of note, it does not discuss the legal issues associated with state-level initiatives to legalize marijuana for recreational use. Until 1937, the growth and use of marijuana was legal under federal law. The federal government unofficially banned marijuana under the Marihuana Tax Act of 1937 (MTA; P.L. 75-238). The MTA imposed a strict regulation requiring a high-cost transfer tax stamp for every sale of marijuana, and these stamps were rarely issued by the federal government. Shortly after passage of the MTA, all states made the possession of marijuana illegal. The Controlled Substances Act (CSA), enacted as Title II of the Comprehensive Drug Abuse Prevention and Control Act of 1970 (P.L. 91-513), placed the control of marijuana and other plant, drug, and chemical substances under federal jurisdiction regardless of state regulations and laws. In designating marijuana as a Schedule I controlled substance, this legislation officially prohibited the manufacture, distribution, dispensation, and possession of marijuana. As part of the CSA, the National Commission on Marihuana and Drug Abuse, also known as the Shafer Commission, was established to study marijuana in the United States. Specifically, this commission was charged with examining issues such as (A) the extent of use of marihuana in the United States to include its various sources of users, number of arrests, number of convictions, amount of marihuana seized, type of user, nature of use; (B) an evaluation of the efficacy of existing marihuana laws; (C) a study of the pharmacology of marihuana and its immediate and long-term effects, both physiological and psychological; (D) the relationship of marihuana use to aggressive behavior and crime; (E) the relationship between marihuana and the use of other drugs; and (F) the international control of marihuana. The Shafer Commission, in concluding its review, produced two reports: (1) Marihuana: A Signal of Misunderstanding , and (2) Drug Use in America: Problem in Perspective . In its first report, the Shafer Commission discussed the perception of marijuana as a major social problem and how it came to be viewed as such. It made a number of recommendations, including the development of a "social control policy seeking to discourage marihuana use, while concentrating primarily on the prevention of heavy and very heavy use." In this first report, the Shafer Commission also called the application of the criminal law in cases of personal use of marijuana "constitutionally suspect" and declared that "total prohibition is functionally inappropriate." Of note, federal criminalization and prohibition of marijuana was never altered, either administratively or legislatively, to comply with the recommendations of the Shafer Commission. In its second report, the Shafer Commission reviewed the use of all drugs in the United States, not solely marijuana. It examined the origins of the drug problem in the United States, including the social costs of drug use, and once again made specific recommendations regarding social policy. Among other conclusions regarding marijuana, the Shafer Commission indicated that aggressive behavior generally cannot be attributed to marijuana use. The Shafer Commission also reaffirmed its previous findings and recommendations regarding marijuana and added the following statement: The risk potential of marihuana is quite low compared to the potent psychoactive substances, and even its widespread consumption does not involve social cost now associated with most of the stimulants and depressants (Jones, 1973; Tinklenberg, 1971). Nonetheless, the Commission remains persuaded that availability of this drug should not be institutionalized at this time. At the conclusion of the second report, the Shafer Commission recommended that Congress launch a subsequent commission to reexamine the broad issues surrounding drug use and societal response. While a number of congressionally directed commissions regarding drugs have since been established, no such commission has been directed to review the comprehensive issues of drug use, abuse, and response in the United States. Going forward, policy makers may debate the utility of a complete re-examination of federal drug policy or, more narrowly, federal marijuana policy. Over the past few decades, some states have deviated from an across-the-board prohibition of marijuana. Evolving state-level positions on marijuana include decriminalization initiatives, legal exceptions for medical use, and legalization of certain quantities for recreational use. Marijuana decriminalization differs markedly from legalization . A state decriminalizes conduct by removing the accompanying criminal penalties; however, civil penalties remain. If, for instance, a state decriminalizes the possession of marijuana in small amounts, possession of marijuana still violates state law; however, possession of marijuana within the specified small amount is considered a civil offense and subject to a civil penalty, not criminal prosecution. By decriminalizing possession of marijuana in small amounts, states are not legalizing its possession. In addition, as these initiatives generally relate to the possession (rather than the manufacture or distribution) of small amounts of marijuana, decriminalization initiatives do not conflict with federal law enforcement's priority of targeting high-level drug offenders, or so-called "big fish." Decriminalization initiatives by the states do not appear at odds with the CSA because both maintain that possessing marijuana is in violation of the law. For example, individuals in possession of small amounts of marijuana in Massachusetts—a state that has decriminalized possession in small amounts—are in violation of both the CSA and Massachusetts state law. The difference lies in the associated penalties for these federal and state violations. Under the CSA, a person convicted of simple possession (1 st offense) of marijuana may be punished with up to one year imprisonment and/or fined not less than $1,000. Under Massachusetts state law, a person in possession of an ounce or less of marijuana is subject to a civil penalty of $100. In recent years, several states have decriminalized the possession of small amounts of marijuana; however, some of these states, such as New York, continue to treat possession of small amounts of marijuana as a criminal offense under specific circumstances. In New York, the possession of small amounts of marijuana is still considered a crime when it is "open to public view." In 2010, nearly 55,000 individuals in New York State were arrested for criminal possession of marijuana in the fifth degree, a misdemeanor in New York State. In November 2014, New York City (NYC) Mayor de Blasio and NYC Police Commissioner Bratton announced a change in marijuana enforcement policy; individuals found to be in possession of marijuana (25 grams or less) may be eligible to receive a summons instead of being arrested.