As part of a larger scheme to regulate drugs and other controlled substances, federal law prohibits the cultivation, distribution, and possession of marijuana. No exception is made for marijuana used in the course of a recommended medical treatment. By categorising marijuana as a Schedule I drug under the Controlled Substances Act (CSA), the federal government has concluded that marijuana has "no currently accepted medical use in treatment in the United States." This book will review the federal government's constitutional authority to enact the federal criminal prohibition on marijuana; highlight certain principles of federalism that prevent the federal government from mandating that states participate in enforcing the federal prohibition; consider unresolved questions relating to the extent to which state authorisation and regulation of medical marijuana are pre-empted by federal law; and assess what obligations, if any, the U.S. Department of Justice (DOJ) has to investigate and prosecute violations of the federal prohibition on marijuana.