This paper estimates the direct effects of investment tax credits on firms' production behavior and the additional indirect effects arising from agglomeration economies. Exploiting a change in tax credit rates by firm size in Germany, I find that manufacturing firms increase capital and employment, with labor demand in information and communication technology-intensive industries shifting towards college-educated workers. Using geolocation data, I show that agglomeration benefits lead to a sizable further firm production expansion with these benefits materializing within distances of 5 kilometers. Worker flows from the service sector and from non-employment, rather than between manufacturing firms, explain the employment effects.