This chapter analyses the concept of localism and its multiple and contested meanings for providing a theoretical understanding of the 'local' and of 'localism'. It argues that the meaning of localism lies at an institutional-representational-territorial nexus with its own contested and continually changing ontologies, identities and boundaries. The idea of localism as preferring the local is often view from within locality, as expression of the desire for self-determination and/or resistance against outside forces. Localism as a response to environmental degradation and climate change has been seen as the practical embodiment of sustainable development. The tension between an instrumental and a cultural concept of the local, and between managerial and emancipatory ways of seeing it, has been used to frame the way the concept of localism is developed and used. Localism may use the idea of local as banner for resistance or efficient form of organisation, but a locality is social world composed of diverse local and extra-local agencies.