It is difficult to justify tax incentives within the existing economicsliterature on tax competition. We develop a model in which communitiesare interested in attracting firms not only for their own capital butalso for the concentration externalities, a form of agglomerationeconomies, their location bestows on existing firms. We find that itis efficient in this case for communities to offer tax incentives,defined as a tax rate below the benefit tax level, to firms. We presentthe recent relocation of the Boeing Corporation's headquarters fromSeattle to Chicago as a case study.