There are currently eighteen American states plus Washington D.C. that have medical marijuana laws. These laws were designed to decriminalize and legalize the use of marijuana for approved medical conditions and purposes. The federal government has not recognized state medical marijuana laws as legitimate protections for the medical use of the drug. The states continue to pass medical marijuana legislation via the citizen initiative process and through the formal legislative process. The spread of medical marijuana policies in the American states has taken place over the course of nearly two decades and will likely continue. This research examines the spread of these policies and investigates the intrastate and interstate political forces that may have contributed to decision to adopt medical marijuana laws in multiple states.