To many, cannabis is a recreational drug; to some, it is a medicine. Now, it is increasingly seen as a crop, to be grown in quantity and engineered for better traits—not just pharmacological effects, but also fiber content and the rapid, efficient growth that makes a plant useful for biofuels. This month, in a special issue of Critical Reviews in Plant Sciences, researchers delve into all aspects of cannabis biology and ecology. The work sheds light on how the plant has diversified since it was first grown 8500 years ago in Eurasia.