This paper proposes a new method to measure ethnolinguistic diversity and offers new results linking such diversity with a range of political economy outcomes -- civil conflict, redistribution, economic growth and the provision of public goods. We use linguistic trees, describing the genealogical relationship between the entire set of 6,912 world languages, to compute measures of fractionalization and polarization at different levels of linguistic aggregation. By doing so, we let the data inform us on which linguistic cleavages are most relevant, rather than making ad hoc choices of linguistic classifications. We find drastically different effects of linguistic diversity at different levels of aggregation: deep cleavages, originating thousa...