The majority of states have legalized the use of marijuana at least for medical purposes, and about a dozen of those states have gone further, legalizing it for recreational use. Either step would have been almost inconceivable just a few decades ago. But marijuana remains an illegal “controlled substance” under a 1970 federal law, so those who sell or grow it could still face federal prosecution. How can state and federal laws be in such conflict? And could federal law put the new state laws in jeopardy at some point? Marijuana Federalism: Uncle Sam and Mary Jane explores the legal and policy issues presented by the conflict between federal and state marijuana laws, ranging from constitutional questions about the scope and nature of federal power to questions of enforcement discretion and state‐level regulation. While the nation’s federalist structure presents complications when federal and state preferences conflict, it could also provide the foundation for more sensible drug policy in the 21st century. Please join us for a discussion of this new book, featuring its editor and one of its contributors.