Effective professional development occurs in learning communities where teachers co-construct knowledge with peers about teaching and learning by engaging in meaningful activities. However, only a few studies have examined the complex nature of discourse, participation, and learning in professional development contexts. Grounded in the notion of "communities of practice," this study investigated how middle and high school teachers who participated in a series of professional development activities on implementing Socratic circles in Grades 7-12 classrooms negotiated participation and membership in building a community of practice in and through Socratic circles. Twenty-three teachers were audio- and video-recorded when they participated in 10 discussions as part of a semester-long experience. The discourse analysis demonstrates how the participants negotiated different forms of participation in Socratic circles, and implications for teacher educators and teachers are offered.