I work with high school mathematics teachers in professional learning communities within and across schools. Our project intiates and helps to sustain the communities through providing initial facilitation of the community, and through gradually handing over this facilitation role to school-based facilitators (teachers). We then work with the facilitators in a professional learning community to build their facilitation practices. Our research focuses on what and how the teachers learn in the communities, shifts in their practices emanating from this learning and describing facilitation practices in professional learning communities.