On July 1, 2011, approximately four hundred prisoners in California’s Pelican Bay State Prison began a sustained hunger strike. Most of these prisoners had been in total solitary confinement, under conditions of extreme sensory deprivation, for five or more years; a few had been in isolation for more than twenty years. The prisoners vowed to refuse food until five core demands were met. These demands were poignantly simple, including provision of warm clothes for their one hour per day of outdoor exercise in the “dog run,” permission to make one phone call per week, a supply of adequate food, and the possibility that indefinite assignment to total solitary confinement might be reviewed after some number of years. The first phase of the strike lasted three weeks, until correctional officials promised to reconsider the state’s segregation policies. Drawing on previously unavailable videos of negotiations between the strike leaders, published media interviews and correspondence with hunger strikers and correctional administrators, and contemporary news reports of the events, this article examines the history, tactics, and implications of the massive hunger strike that took place in California’s highest-security prison (a supermax) in the summer of 2011. The article argues that the strike embodies a legitimacy paradox. Although the history of prison organizing in California, and of hunger strikes around the world, suggests that prisoners willing to die to protest prison injustices also undermine the legitimacy of the system inflicting those injustices, the 2011 California prisoners on hunger strike repeatedly invoked the broader legitimacy of the US prison system. Indeed, the article argues that, although prisoners drew on an international dialogue about basic human rights and appropriate tactics of resistance to rights violations, the US supermax context limited the reform conversation to small, mundane debates about the language of rules and the slight adjustments in privileges provided to prisoners. But that very conversation ultimately highlighted the extremity of the conditions in supermax confinement, driving unprecedented and sustained media and legal attention to the use of supermaxes, across the United States and internationally, and inspiring another larger (thirty thousand prisoners participated at the peak) and longer (sixty days) hunger strike in 2013.