The concept and application of professional learning communities has become widespread in approaches to large-scale system and school improvement. A professional is someone with expertise in a specialized field, an individual who has not only pursued advanced training to enter the field, but who is also expected to remain current in its evolving knowledge base. Learning suggests ongoing action and perpetual curiosity. This chapter discusses one approach to teacher-led professional learning - Ontario's Teacher Learning and Leadership Program (TLLP) - which may have relevance to rethinking and developing communities of professional learners. Successful teacher applicants receive training, support and funding for their TLLP projects. TLLP projects vary considerably in size. Participation in such teacher-led professional learning appears to be highly beneficial for teachers' learning and practice. In addition to supporting the TLLP teacher leaders' own learning, a goal of the TLLP is for teachers to lead the professional learning of other teachers.