Amnesty International does not seek to minimize the challenges faced by prison administrators in dealing with prison gangs and individuals who are a threat to institutional security and recognizes that it may sometimes be necessary to segregate prisoners for disciplinary or security purposes. However, all measures must be consistent with states’ obligation under international law and standards to treat all prisoners humanely. In recognition of the negative effects of such treatment, international and regional human rights bodies and experts have called on states to limit their use of solitary confinement, so that it is imposed only in exceptional circumstances for as short a period as possible. As described below, Amnesty International considers that the conditions of isolation and other deprivations imposed on prisoners in California’s SHU units breach international standards on humane treatment. The cumulative effects of such conditions, particularly when imposed for prolonged or indefinite periods, and the severe environmental deprivation in Pelican Bay SHU, in particular, amounts to cruel, inhuman or degrading treatment, in violation of international law.