The notion of working across boundaries attracts both practical interest from people in government, and theoretical interest from scholars. Much emphasis has been placed on notions of inter-organisational, inter-jurisdictional and inter-sectoral working, and a range of terms have emerged to capture this phenomenon: horizontal coordination, joined-up government, collaboration, whole-of-government, holistic government, collaborative governance and so on. However, there is a core element to all these terms – the notion that we must traverse boundaries to achieve goals.Most of the new ideas about public management which have emerged over the last decade or so have put the notion of working across boundaries front-and-centre. Indeed, Kelman (2007) has argued that the topics of collaboration across government agencies and between government, private and non-government organizations are the 'most-discussed questions involving the performance of public institutions and achievement of public purposes' (p.45).In this paper we provide an overview of the literature on working across boundaries to help answer two key questions: First, why has this notion emerged? Second, what are the critical enablers and barriers which help us to understand how this works (or not)?