Abstract The ‘paradox’ in this title refers to a set of contradictions that sit at the heart of education policy in many school systems. Policymakers in these systems want things that, if not inherently at odds, are nevertheless in tension— such as a tightly defined set of national standards and a broad and balanced curriculum; academic stretch for the most able and a closing of the gap between high and low performers; choice and diversity and equity; and so on. The ‘quest’ is for leaders and leadership to resolve these tensions in practice. School autonomy policies have placed huge power in the hands of, and pressure on the shoulders of, leaders in high-autonomy–highaccountability quasi-market systems. Research has often focused on the values, characteristics and behaviours of effective leaders and leadership teams, but there can also be a darker, toxic side to leadership, and it is clear that leadership agency is constrained by the influence of hierarchy and markets. Meanwhile, policymakers have become increasingly concerned with how to foster innovation as they wrestle with the question of how education might adapt to the needs of an increasingly complex, globalised world. Critics argue that change has been constrained by narrowly defined criteria for success and an instrumental focus on improvement, leading to a crisis of legitimacy. What seems clear is that change will require new approaches that somehow unlock leadership agency while supporting the development of new forms of leadership that can—and consistently do—resolve the paradox. This lecture will focus on England’s efforts to create a ‘self-improving school system’, which can be seen as one response to these issues. It will draw on the findings from a three-year study of the changes in England to draw out the wider implications for research and policy on leadership and school system reform.