School leaders' tasks have become increasingly complex, as a result of globalization, a shift towards knowledge based economies, greater student diversity and an increased government focus on education policy reforms targeting and affecting schools. The role of school principals has moved from administrative leadership towards focusing on student outcomes, with more autonomy and accountability, and increased responsibilities for implementing policy reforms in schools and classrooms. This article focuses on how policies can ensure that school leaders contribute to school improvement. It builds on an international OECD study on school leadership which analyzed practices across 22 education systems in 2008 and explores developments since to propose policy options that can contribute to support the professionalization of school leadership. Among the key strategies suggested that many countries have been taken up are: clarifying the role of school leaders based on the tasks that make most difference on school outcomes; ensuring there is specialized training and development: that working conditions are attractive to ensure that there are quality professionals in exercise and that it is a sustainable profession that is well supported.