VA set an ambitious goal for ending homelessness among Veterans by 2015. Housing Urban Development-VA Support Housing [HUD-VASH] and Grant and per Diem [GPD] are two primary VA housing programs to help Veterans exit homelessness. Substance abuse among Veterans in VA housing is a major risk factor for worsening psychopathology and housing instability. Despite recent adoption of a Housing First approach, many VA housing programs lack the staff infrastructure to manage substance use disorders (SUDs). This is a significant problem as 60% (conservative estimate) of Veterans in VA housing have SUDs and these Veterans show greater psychopathology compared to their counterparts without SUDs. These issues warrant substantial need for SUD programs in VA housing that are efficient to deploy, easily layered onto existing services, and require minimal staff to operate. The current study addresses this current void in VA treatment services in that it investigates the effectiveness, implementation process, and cost estimate of treatment of an adaptation of motivational interviewing, an empirically supported intervention with strong impact on reducing substance use and enhancing treatment engagement, in a group format, referred to as Group Motivational Interviewing (GMI) for Veterans with SUDs in VA housing. Data from this project, if shown to be promising, will establish the basis of a GMI dissemination and implementation course of action for highly vulnerable homeless Veterans in VA housing for achieving their greatest success in attaining housing stability.