Five years into the twenty-first century, more than 9 million people are held in custody in more than two hundred countries around the world. Several times that number are directly affected by prisons, either because family members are incarcerated or because they work in prisons; or are involved in their planning, construction, or maintenance; or otherwise service the needs of prisoners and staff. The use of imprisonment is, by any standards, not merely a substantial instrument of social and penal policy; it is also a major industrial and organizational undertaking, and most current signs indicate that it is becoming even more so.