The current study, through a randomized controlled design, will evaluate the effectiveness of peer support, as compared to usual care and to an equivalent amount of support offered by peer case managers and non-peer recovery mentors, in reducing hospital days and readmissions and in promoting recovery and community inclusion among adults with mental illnesses with histories of multiple hospitalizations. The current study evaluates the cost-effectiveness of adding peer support to the array of services available to persons with serious mental illnesses who have histories of multiple hospitalizations and will test a theoretical model of the active ingredients of peer support, focusing specifically on the roles of 1) instillation of hope through positive self-disclosure; 2) role modeling of self-care and exploring new ways of using experiential knowledge; and 3) a trusting relationship characterized by acceptance, understanding, and empathy with conditional regard.