Despite decades of successful implementation at the K-12 level, cooperative learning (CL) has been slow to catch on at the college level. Resistance by instructors and students alike has slowed its diffusion. Some resistance stems from poor experiences with CL, but potential adopters often fail to realize that effective CL rests on a set of principles that are not intuitively obvious. Drawing on research on group processes and CL, we discuss what instructors need to do to implement CL successfully. We focus on a three-stage model of group formation and development, the components of successful group processes, how these components respond to typical students' complaints, instructors' roles in group operations and processes, and how these roles can best be carried out. (Contains 3 tables.)