This discussion of cooperative second language learning describes the approach in terms of response to three questions: WHO? WHAT? and WHY? The first section "WHO: Major Directors and Actors," chronicles the evolution of cooperative learning in general and cooperative language learning in particular, citing some specific methods and the individuals who developed and promoted them. The second section, "WHAT: Characteristics and Competitors," begins by defining some major paradigms of cooperative learning: Aronson's Jigsaw Classroom; DeVries' Teams-Games-Tournaments; Slavin's Student Teams and Academic Divisions; and the Group Investigation approach. This form of learning is then contrasted with competitive and individualistic learning approaches, especially with regard to the structuring of rewards and incentives. Commonalities between the three learning approaches are also examined. The third section looks at evidence of the efficacy of cooperative learning, citing research and theory on its use of comprehensible input, its efficiency, the effective use of social interaction, and its authenticity and realistic grounding. Objections to the use of cooperative learning in second language instruction are also noted and rebutted. These include the criticisms that students can acquire flawed language from peers, that cooperative learning promotes classroom chaos, and that native language use or code-switching will be tolerated by peers. Four types of instructional materials are described: manufactured; teacher-developed; teacher-adapted; and authentic. (MSE)