System leaders are those headteachers who are willing to shoulder system-wide roles in order to support the improvement of other schools as well as their own. As such, system leadership is a new and emerging practice that embraces a variety of responsibilities that are developing either locally or within discrete national networks or programmes that, when taken together, have the potential to contribute to system transformation. Because this is an emerging practice, there has been no attempt to date to document how system leadership is being enacted and is evolving across the English education system. This article elaborates the concept of system leadership and illustrates its potential power as a catalyst for systemic reform in three ways. First, it not only provides an initial conceptualisation of system leadership based on the contemporary literature and recent policy announcements but also raises a series of concerns about the way the concept is being interpreted. Second, by drawing on responses provided by local authorities, the Department for Education and Skills (DfES), a range of national agencies and professional associations as well local and national networks of headteachers and teachers, it maps the system leadership landscape in England current in 2006 by proposing a taxonomy of roles that system leaders are currently assuming. Third, and based on these analyses and research with leading headteachers, it locates system leadership within the literature on systems theory and leadership, proposes a potential model for system leadership and explores the tensions involved in developing the concept further.