This paper is about the debate over the role of language and culture in socio-economic development. Drawing on his experience of Ireland, the author examines the rich historical tradition of debate about the positive role which language can play in national development, and suggests a theoretical grounding for those arguments. The elaboration of such a theoretical basis is essential as a counterbalance to powerful and dominant global forces which engage in, as Stephen May puts it, “the denunciation of ethnicity”. Those pursuing these arguments have frequently used a form of economic Darwinism in order to justify the marginalisation or extermination of threatened languages or to oppose multilingualism generally. This paper lays out the foundations of an alternative approach which posits that all languages and cultures, regardless of their status or numerical size, can be integrated into processes of socio-economic development, and that none is inherently anti-development. It is hoped that the arguments presented here will also stimulate debate about the nature of the concept of development itself, and facilitate closer integration of the often distinct disciplines of language planning and policy and socio-economic development.