Social interdependence theory has provided a conceptual framework to understand cooperation and competition through a common mechanism: Social interdependence, i.e., the mechanism whereby the outcomes of individuals in a group are affected by the actions of the other group members. Positive social interdependence is the set of rules, norms, or practices that requires all group members to contribute to a common goal in order to fulfill individual goals. Negative social interdependence requires that some members fulfill their goals to the detriment of others’ goals. We review the research showing how social interdependence affects group members’ perceptions and behaviors, which in turn influence their learning outcomes. We focus on cooperation and the work that showed how cooperation requires positive goal interdependence, but also group members’ responsibility and accountability, interactions directed toward the promotion of the partners, the use of social skills, and critical reflection upon group processes. Then we turn to the literature on cooperative methods in education, and we provide evidence that they favor learning outcomes, psychological and social adjustment, and positive relationships, as compared to competitive and individualistic methods. However, cooperation is vulnerable to threatening social comparison, and we provide evidence that interactions among group members that focus on relative status instead of the task may reduce the beneficial effects of cooperation. Finally, we report an intervention study that illustrates how the implementation of cooperative methods requires training and promotion.