In this article, I have three major aims. First, I examine in detail the role that changes to legal policies and practice have played in the rise of mass incarceration. I look at four distinct aspects of legal change and argue that the law (and legal change) in these varied forms is the engine that has driven prison growth and, therefore, must be addressed in explanations of this phenomenon. This discussion leads to my second major goal, which is to move beyond national-level explanations of American mass incarceration and call for a more unified empirically based understanding that highlights the localized social, cultural, and political factors that have contributed to the imprisonment explosion. I conclude by exploring how this kind of theorization provides a road map to a more localized policy reform strategy that aims to reduce our reliance on incarceration.