This chapter explores the origins, evolution, and effectiveness of the climate movement. The climate movement that emerged within civil society in the early years of the twenty-first century is highly heterogeneous, although it is united in calling on officials and policymakers to adopt policies that reduce anthropogenic greenhouse gas emissions. This movement consists of a bewilderingly diverse, dynamic and fluid variety of actors that include individuals, civil society organisations, social movement organisations and networks that often overlap and defy categorisation into separate, strictly defined and stable groupings. Many analysts find it useful to at least distinguish between the climate movement’s two major ‘wings’ or ‘streams’: the more moderate wing (or ‘climate action’ wing) working towards reforming global capitalism by calling for the decarbonisation of the global economy, and the system-critical ‘radical climate justice’ wing that sees climate change as one of many manifestations of a much wider crisis that can only be resolved by fundamental system change. This chapter provides an overview of the ‘war of position’ between these opposed two wings of the climate movement, and locates ecosocialist activists within the radical climate justice wing. It introduces the concept of ‘false solutions’ and also discusses the dangers of trasformismo that members of the ‘climate action’ wing leave themselves open to as they collaborate with policymakers who aim to implement ‘market solutions’ (such as carbon trading) as instruments for reducing greenhouse gas emissions.