© The Author(s) 2019. Thirty-three U.S. states and the District of Columbia (DC) have legalized the use of marijuana for medicinal purposes and 10 states and DC have legalized marijuana for adult recreational use. This mirrors an international trend toward relaxing restrictions on marijuana. This article analyzes patterns in marijuana laws across U.S. states to shed light on the social and political forces behind the liberalization of marijuana policy following a long era of conservatism. Data on U.S. state-level demographics, economic conditions, and cultural and political characteristics are analyzed, as well as establishment of and levels of support for other drug and social policies, to determine whether there are patterns between states that have liberalized marijuana policy versus those that have not. Laws decriminalizing marijuana possession, as well as those authorizing its sale for medical and recreational use, follow the same pattern of diffusion. The analysis points to underlying patterns of demographic, cultural, economic, and political variation linked to marijuana policy liberalization in the U.S. context, which deserve further examination internationally.