System leadership is a developing concept and practice increasingly seen as a tool for school improvement, as policymakers switch from traditional top-down reform to professional models of schools working collaboratively. System leadership is being championed by the Scottish College for Educational Leadership (SCEL), but is still in its infancy in Scottish education. Adopting an international perspective on system leadership, but with reference to the Scottish context, the paper aims first, to clarify the concept and its various connotations, and to focus on the notion of headteachers and other school-level professionals as system leaders. Secondly, it goes on to describe the range of roles that system leaders can play and how these present a degree of choice--and a trajectory--for head teachers in choosing appropriate roles that reflect their expertise, experience, self-efficacy, credibility, and interest. Finally, adopting a critical stance towards the concept and practice of system leadership--to date the focus has been more on roles and less on substantive capacity building competences required by system leaders for school improvement--the paper redresses the imbalance.