Collaboration is an underused teaching strategy despite its benefits and the call for curriculums worldwide to increase its use. To aid in discovering why the strategy is underused, more information was needed about the implementation of collaboration in the mathematics classroom. The purpose of this study was to investigate mathematics teachers' perceptions and experiences when implementing collaboration in their classrooms. The conceptual framework that grounded this study was Vygotsky's social constructivism. Data for the basic qualitative study were collected through 12 interviews with mathematics teachers in California, Oregon, and Washington who have implemented collaboration. Through inductive analysis, seven themes emerged which included the procedures, grouping methods, group work skills, and classroom environment teachers use to implement collaboration as well as the issues teachers face and the benefits teachers outlined when using collaboration. The findings may contribute to social change as they provide school administrators with pertinent information on how to support teachers in implementing collaboration successfully. By providing more professional development on collaboration to teachers, students may gain the benefits from the successful implementation of collaboration in the mathematics classroom. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]