A growing body of empirical urban economic studies suggests that agglomeration and accessibility externalities are important sources of the uneven distribution of economic activities across cities and regions. At the same time, little is known about the importance of agglomeration economies for the actual location behavior of rms. is is remarkable, since theories that underlie agglomeration economies are microeconomic in nature. In a case study of the Dutch province of South Holland, we analyze micro-level data to determine the extent to which relocation decisions are dependent on accessibility and agglomeration externalities when controlling for rm characteristics. ese externalities are measured with location attributes for both own-sector localization and urbanization economies and for proximity to transport infrastructures. e results con rm that rm relocation behavior is affected much more by rm-level attributes (size, age, and growth rate) than by agglomeration and accessibility attributes. Still, accessibility and agglomeration are signi cantly attached to rm relocations, though their effects vary over sectors. Own-sector and generalized external economies are more important for a rm's location choices than proximity to transport infrastructure.