We investigate firms' incentives to locate in the same region to gain access to a large pool of skilled labor. Firms engage in risky R&D activities and thus create stochastic product and implied labor demand. Agglomeration in a cluster is more likely in situations where the innovation step is large and the probability for a firm to be the only innovator is high. When firms cluster, they tend to invest more and take more risk in R&D compared to spatially dispersed firms. Agglomeration is welfare maximizing, because expected labor productivity is higher and firms choose a more effcient, technically diversified portfolio of R&D projects at the industry level.