Specialized interventions, such as police and jail diversion, mental health courts, specialized probation, forensic assertive community treatment, designed to engage justice-involved persons with serious mental illnesses, have expanded over the past two decades. Some of these "first generation" interventions have demonstrated efficacy and several have earned recognition as evidence-based practices. Yet, overall, they have not appreciably reduced the prevalence of persons with serious mental illnesses involved in the criminal justice system. To understand how to make the next generation of interventions more effective, a survey of a national sample of community-based programs serving these clients was conducted. Surveys were completed on-line by direct service staff affiliated with 85 programs and collected data on the characteristics and needs of the client base; characteristics and challenges associated with difficult-to-engage clients; service needs and obstacles; and recommendations for improving program effectiveness. A sample of the survey participants (19 programs from 18 states) attended a day-long workshop to discuss the survey findings and ways to improve treatment adherence and client services. Respondents reported that their clients have a constellation of problems with different origins, etiologies, and symptoms, often crossing over the boundaries of mental illness, addictions, and antisocial pathologies. According to the practitioners working with justice-involved clients with mental illnesses, responding effectively requires knowledge of many different problems, expertise to respond to them, and an understanding of how these problems interact when they co-occur. The poly-problems of these clients suggest the need for an integrated and comprehensive approach, which is challenged by the fragmented and diverse ideologies of the behavioral health, criminal justice, and social service systems.