This article reviews a growing literature investigating how "immigrant" diversity relates to urban economic performance. As distinct from the labor-supply focus of much of the economics of immigration, this article reviews work that examines how growing heterogeneity in the composition of the workforce may beneficially or harmfully affect the production of goods, services, and ideas, especially in regional economies. Taking stock of existing research, the article argues that the low-hanging fruit in this field has now been picked and lays out a set of open issues that need to be taken up in future studies in order to fulfill the promise of this work.