The overall number of inmates in the Bureau of Prisons' (BOP) three main types of segregated housing units, Special Housing Units (SHU), Special Management Units (SMU), and Administrative Maximum (ADX), increased at a faster rate than the general inmate population. Inmates may be placed in SHUs for administrative reasons, such as pending transfer to another prison, and for disciplinary reasons, such as violating prison rules; SMUs, a four-phased program in which inmates can progress from more to less restrictive conditions; or ADX, for inmates that require the highest level of security. From fiscal year 2008 to February 2013, the total inmate population in segregated housing units increased approximately 17 percent, from 10,659 to 12,460 inmates. By comparison, the total inmate population in BOP facilities increased by about 6 percent during this period. This book examines the trends in the BOP's segregated housing population; the extent to which the BOP centrally monitors how prisons apply segregated housing policies; and the impact segregated housing has on institutionalised safety and inmates.