This thesis deals with the economic analysis of population diversity, specifically diversity in terms of people's countries of origin. We propose an index of birth-place diversity for the work force of 195 countries in the years 1990 and 2000. We show that birthplace diversity is a new dimension of population diversity that is conceptually and empirically distinct from ethno-linguistic and genetic measures of diversity and, unlike these, is positively correlated with long-run economic output. This effect is larger for skilled immigrants in richer countries and robust in a SLS setting. We also find the productive effect of diversity to be larger for immigrants who are culturally close (but not too close) to natives and those who come from r...