Stress reactions have been considered a significant problem for providers of emergency services in the aftermath of traumatic events known as Critical Incidents. A group crisis intervention technique known as Critical Incident Stress Debriefing (CISD) has become known as a useful approach to mitigate the stress reactions considered common to these events. In this dissertation, CISD was examined using standardized stress outcome measures in two groups of emergency medical and fire/rescue providers. The CISD process builds on work from a symbolic-interaction, and field theory perspective. All subjects in the study were emergency services providers who had been exposed to emergency rescue operations that met operationalized definitions of exposure to a critical incident. Subsequent selection by the various groups led some of the subjects to engage in the CISD process, while others did not. Demographic and qualitative data were obtained about the various rescue events. A Quasi-experimental, non-equivalent, pretest-posttest design measured psychosocial stress response using the Impact of Event and the Everly Stress Inventory. Data were obtained at measurements directly pre-intervention and again at 60 days. Data were analyzed using qualitative and multiple regression techniques. The data were suggestive that the CISD process was helpful in reducing psychosocial stress through inculcating a moderate increase in a sense of control about the critical incident. Recommendations are made as to directions for further study.