What underpins the legitimacy of the prison system in the 21st century? Despite numerous challenges and setbacks, there is still a widespread belief that prisons can be improved in a socially progressive way. Even today, 'model prisons' are being built that seek to fix the shortcomings and failures of their predecessors, as if past failures were due to a lack of imagination, determination or resources. The aim of creating model prisons is not new: it dates back to the early 19th century. Ranging from England to Switzerland and Spain, from Russia to China and India, Carceral Utopia documents a rich, global history of ambitious efforts to create model prisons – places of confinement initially lauded for their progressive ideals but later revealed as fiascos. At the end of this journey through time and space, it will not suffice merely to highlight the gap between plans and realities, or even to dispel the illusion that model prisons could not live up to their claims. We need to ask why, despite so many failures, these institutions are still being built today. Might it be that their many obvious shortcomings conceal a covert success?