This chapter assess the positive value of group work in achieving treatment goals when treating mental disorders in offenders generally and sexual offenders specifically in a clinical setting. The chapter provides a brief overview of the relevant aspects of the general clinical literature dealing with various Axis 1 and Axis 2 disorders other than those that are the focus of interventions with offenders. The authors then consider what the evidence tells us about the treatment and group process factors associated with various, non-sexual offenders. Finally, they give attention to the emerging literature on the influence of treatment process issues, with a specific focus on group processes, with sexual offenders. The features of the delivery of treatment discussed are: (1) the style or characteristics of the therapist; (2) the therapeutic alliance between the therapist and client; and (3) the climate of the group. The latter is included because most programs for offenders are delivered in groups. It is important to note that the therapists' style, and the way the clients perceive the therapists' style (which are not always a match), appear to be the major determinants of both the therapeutic alliance and the group climate. (PsycINFO Database Record (c) 2019 APA, all rights reserved)