Study Design: This study uses a two-arm, multi-centered randomized controlled clinical trial design to compare the GIST treatment to an alternative treatment, in which participants are presented information from the GIST treatment program without the group process. A total of 192 military, veteran and civilian participants with mild to moderate TBI will be enrolled by six centers. Measures will be collected at baseline, post-treatment, and 3 months post-treatment. Videotapes of participants will be evaluated for social competence by blinded independent raters, and progress on individualized social skills goals will be assessed. Replicable training of group leaders will include a 2 ½ day in-person workshop followed by feedback during a pilot of the intervention and alternative intervention. The fidelity of the intervention will be assessed by independent raters using a standardized instrument to ensure that the intervention is implemented consistently. Results of this study will be disseminated to relevant stakeholders via presentations and publications. By the end of this study, the field will have definitive evidence about the effectiveness of a group social competence intervention for people with TBI.