Critical thinking has long been identified as an innovative skill and as an upshot of learning process that is essential to prepare students for post-secondary education. EFL/ESL researchers have persistently focused on effective learning strategies that can train good language learners and encourage them to improve themselves as thinkers. One of the academic skills recognized as a determiner of learning is critical thinking (CT). Likewise, one of the effective instructional methods which can enhance and improve learners’ critical thinking ability and their problem-solving skills is cooperative learning (CL). This book investigated the effect of learning together model of cooperative learning on the Iranian EFL learners’ critical thinking ability. Syllabus designers, textbook writers, EFL/ESL teachers, learners, teacher trainers, methodologists, language schools and colleges will expectantly find this book helpful.