This report examines past and continued use of solitary confinement by the Colorado Department of Corrections (CDOC) to manage mentally ill prisoners; considers the moral, fiscal, safety and legal implications of CDOC’s continued warehousing of mentally ill prisoners in solitary confinement; and makes recommendations to bring Colorado’s prisons in line with modern psychiatric, correctional and legal standards. The report draws on 18 months of research by the American Civil Liberties Union (ACLU) of Colorado, which included correspondence with mentally ill prisoners housed in solitary confinement by CDOC; analysis of data provided by the CDOC in response to over a dozen public records requests by the ACLU, as well as other publicly available CDOC records; in-depth review of several prisoner mental health files; extensive written and in-person dialogue with CDOC’s executive team; on site visits to CDOC; and multiple consultations with correctional and psychiatric experts.