This dissertation is an investigation of the influence of the promotion of the Irish language on Ireland's socio-economic development. The research question is based on a tradition of understanding of the link between the Irish language and Ireland's socio-economic development, stretching back at least 150 years. Various authors have argued that the promotion of Irish is not only about re-establishing the language as a means of communication, but that it will bring broader social, economic and cultural benefits to Ireland as a whole. In order to investigate the research question, the relationships which these authors posit are interrogated in the light of various bodies of theory in the social sciences (economics, sociology, political economy, development studies and sociolinguistics). A typology of competing approaches to language and development is presented and a theoretical framework appropriate to the analysis elaborated. This framework - the linguistic political economy of development - guides the remainder of the dissertation, which consists of a series of case-studies. In the case-studies, the empirical basis of the relationship between the Irish language and Ireland's socioeconomic development is examined, and the tensions between the competing approaches to language and development are considered. The study concludes by drawing on the findings of the investigation and considers how it has addressed the research question.