May a state authorize the use of marijuana for recreational purposes even if such use is forbidden by federal law? This novel and unresolved legal question has vexed judges, politicians, and legal scholars, and it has also generated considerable public debate among supporters and opponents of “legalizing” the recreational use of marijuana. Under the federal Controlled Substances Act (CSA), the cultivation, distribution, and possession of marijuana are prohibited for any reason other than to engage in federally approved research. Yet 18 states and the District of Columbia currently exempt qualified users of medicinal marijuana from penalties imposed under state law. In addition, Colorado and Washington recently became the first states to legalize, regulate, and tax small amounts of marijuana for nonmedicinal (so-called “recreational”) use by individuals over the age of 21. Thus, the current legal status of marijuana appears to be both contradictory and in a state of flux: as a matter of federal law, activities related to marijuana are generally prohibited and punishable by criminal penalties, whereas at the state level, certain marijuana usage is increasingly being permitted. Individuals and businesses engaging in marijuana-related activities that are authorized by state law nonetheless remain subject to federal criminal prosecution or …