For the purposes of this chapter, "supermax" facilities have the following elements: accommodation that is physically separate or separable from other units or facilities; a controlled environment that emphasizes safety and security through separation from staff and other inmates and restricted movement; and use with prisoners who have been administratively identified as needing such control based on their violent or seriously disruptive behavior in other high-security facilities. The data reported in this chapter were derived mainly from two research projects funded by ESRC and Leverhulme. Regarding effects on prisoners, supermax custody is intended to provide incapacitation and individual deterrence with reference to behavior that threatens safety and security within the prison. Effects that impact law-abiding postrelease behavior are rarely a consideration in supermax custody. This chapter considers some of the differential long-term psychological effects on supermax prisoners. Studies of staff who manage supermax prisoners indicate that the staff rarely use the skills required to handle inmates' problem behaviors, which suggests that they may not be prepared to deal with inmates in the general population of inmates or would too readily recommend that inmates be transferred to supermax custody when they are not easily managed. Regarding the effects of supermax custody on the prison system, the limited research on this issue provides little evidence that such facilities stabilize security and control in the broader prison system, as has been envisioned by its advocates. Regarding the effects of supermax custody on society, there is concern that it will lead to a deterioration of societal standards for measuring "cruel and unusual punishment." 16 notes and 40 references