The claim that American justice system engages in "mass incarceration" is now a cliche, albeit one that seems entirely justified by both the number and rate of people who are behind bars. As a result, a large number of states and the fed­eral government have engaged in wide-ranging reform efforts to shorten senten­ces, divert people from prison, and in general reduce incarceration numbers to more manageable levels. Although these efforts have made modest gains, there has been little discussion of whether their ultimate goal is feasible-reducing incarceration levels to a point where "mass" incarceration is no longer an apt description. This article explores the likelihood of a meaningful, sustained reduction in incarceration rates. It begins by asking what we really mean by mass incarcera­tion and finds that while the definition is surprisingly complex, the label ulti­mately seems justified. Then, using existing and original compilations of data, the article examines some of the less-obvious obstacles to reducing prison popula­tions. In particular, it highlights the difficulty of reducing incarceration rates without addressing the problems created by those convicted of violent crimes, something few reforms have been willing or able to do. It also argues that those who believe prison reform will lead to economic savings-a primary motivation in virtually every state-are misguided, and that illusion of economic savings might ultimately derail the reform efforts. The article then takes a further step and suggests that efforts to decrease incarceration levels will inevitably be frustrated unless the most influential per­son in the creation of mass incarceration, the prosecutor, is induced to play a more central role. To date, reform efforts have routinely targeted everyone in the process except prosecutors, and this article offers both suggestions on why this is so and an argument for why prosecutors are an indispensable part of any change. The article concludes with the sobering prediction that, as useful as recent reforms have been, as currently constructed they will ultimately be inad­equate to erase the mass incarceration label for years to come.