The Instructional Leadership Corps (ILC) is an innovative professional learning project in which teacher leaders in California collaborate to lead sustainable professional development to support implementation of new student standards within their districts. Over more than 4 years, the ILC has served over 100,000 teachers. The responses of these educators to ILC conferences and trainings have been overwhelmingly positive. This brief describes how the ILC has changed the professional development landscape in four communities, offering lessons about how teacher-led learning can motivate shifts in practice, enhance teachers' professionalism and efficacy, and create supportive systems and strategic relationships that can sustain change. [For the full report, see ED603444.]