Complexity is a core feature of most policy issues today and in this context traditional analytical tools and problem-solving methods no longer work. This report, produced by the OECD Observatory of Public Sector Innovation, explores how systems approaches can be used in the public sector to solve complex or "wicked" problems . Consisting of three parts, the report discusses the need for systems thinking in the public sector; identifies tactics that can be employed by government agencies to work towards systems change; and provides an in-depth examination of how systems approaches have been applied in practice. Four cases of applied systems approaches are presented and analysed: preventing domestic violence (Iceland), protecting children (the Netherlands), regulating the sharing economy (Canada) and designing a policy framework to conduct experiments in government (Finland). The report highlights the need for a new approach to policy making that accounts for complexity and allows for new responses and more systemic change that deliver greater value, effectiveness and public satisfaction.