The USA incarcerates thousands of prisoners in long-term or indefinite solitary confinement. This report describes Amnesty International’s concerns about conditions of severe isolation at the United States Penitentiary, Administrative Maximum facility in Colorado. It also examines conditions in Special Management Units and Security Housing Units operated at other federal prison facilities. Amnesty International believes these conditions breach international standards for the humane treatment of prisoners. The report also details disturbing evidence of prisoners with serious mental illness being detained in harsh isolated conditions without adequate screening, treatment or monitoring.