The chapters collected in this volume go beyond the doctrinal debates over whether non-state actors have personality, are subjects or objects of international law, or indeed whether or not they are bound by international obligations. The authors draw on their personal experiences to explain how non-state actors adjust their behaviour in light of international law, how such actors are contributing to the development of international law, and what sort of policies should be adopted towards non-state actors in order to ensure a better framework for the protection of those affected. An expansive definition of the term non-state actor allows the authors to cover the contemporary interactions between a multiplicity of ‘players’: the ICRC, the United Nations, private military companies, Geneva Call and the rebel groups themselves. There is a focus on the development of the UN through international courts and human rights bodies, but the book does not lose sight of the practices that are developing—often in parallel to the legal doctrine. Out of this examination of law and practice, the authors manage to point towards the policies that ought to be considered. Some of these require no changes to the legal framework—only new ways of seeing the issues—while others require not just imagination but concrete steps to realise increased possibilities for holding accountable those who transgress fundamental humanitarian and human rights norms.