This article argues for a particular conceptualisation of teacher leadership; one that enables us to overcome the limitations of established approaches to continuing professional development as a strategy for school improvement by mobilising the massive untapped potential of teachers as leaders of innovation. In this article, teacher leadership is conceived as a key dimension of the role of teachers regardless of special roles and responsibilities in the organisational structures of their schools. Evidence to support this argument is drawn from the International Teacher Leadership project, which has partners in 15 countries as diverse as Kosovo and New Zealand. The International Teacher Leadership project builds on a model developed in the United Kingdom (The HertsCam Network) to develop support for teacher leadership as an educational reform strategy. The article explores the professional learning arising for the teachers and offers a theory of educational innovation within which it is located. (Contains 1 table and 4 figures.)