Cooperative learning is an example of how theory validated by research may be applied to instructional practice. The major theoretical base for cooperative learning is social interdependence theory. It provides clear definitions of cooperative, competitive, and individualistic learning. Hundreds of research studies have validated its basic propositions and demonstrated that cooperative learning (compared with competitive and individualistic learning) increases students' efforts to achieve, encourages positive relationships with classmates and faculty, and improves psychological health and well being. Operational procedures have been derived from the validated theory to implement cooperative learning in university classes, including those needed to implement formal cooperative learning, informal cooperative learning, and cooperative base groups.