The use of group dynamics principles such as group goal-setting, distinctiveness and cohesion has been the basis of a burgeoning area of physical activity (PA) promotion. Recent reviews of literature suggest that these interventions are robust and increase PA in a wide variety of populations. Still, a number of questions remain unanswered in the areas of theory development, intervention implementation, and translation of research into practice. This dissertation includes a series of manuscripts that focus on research, theory, and practice of group dynamics interventions intended to promote PA. Within research, a systematic review of literature explores group dynamics-based PA interventions in terms of generalizability (through RE-AIM evaluation) and the degree to which the interventions use research techniques that are more pragmatic (reflect typical practice) or more explanatory (testing under optimal conditions). This exploration is based on an initial review of 17 interventions that employ group dynamics strategies to increase PA, fitness, and/or adherence. The results suggest that this body of literature includes a range of pragmatic and explanatory trials, but still has gaps in reporting related to external validity. Embedded within the context of a PA promotion program for minority women, the second manuscript addresses a theory-based question—to what degree do group-interaction variables (cooperation, communication, and competition) differentially predict group cohesion over time. The results suggest that friendly competition is the strongest and most consistent predictor of different dimensions of group cohesion while task and socially related communication are consistent predictors of task and socially related cohesion, respectively. Two manuscripts are included in addressing the use of group dynamics principles within practice settings. The first practice manuscript details a small pilot study in which obese, limited income women successfully (p<0.05) limited gestational weight gain to the Institute of Medicine (2009) recommendation of 11-20 pounds. This study attempted to integrate a group dynamics approach into a group visit model for pregnant women. The quantitative findings were promising, but qualitative findings indicated a number of difficulties in implementation. The purpose of the final manuscript was to determine the attributes of the program agents consider when deciding to adopt a PA and fruit and vegetable promotion program and their understanding of key strategies related to group dynamics theory. Delivery agents were able to identify key underlying principles and propose adaptations that align with those principles.Ph. D.