This highly preliminary work attempts to study the multiple drivers of agglomeration phenomena in contemporary economies. First, we propose a tentative taxonomy of agglomeration drivers in which the conditions of knowledge accumulation play a paramount role. Second, we discuss the achievements and limitations of current theorizing on spatial location of economic activities. Third, we propose a simple model of firm agglomeration which is estimated on Italian data. Econometric results highlight the rich intersectoral diversity of agglomeration forces and their relative strength.