The authors provide first evidence on whether the direct relationship between educational mismatch and firm productivity varies across working environments. Using detailed Belgian linked employer-employee panel data for 1999-2010, they find the existence of a significant, positive (negative) impact of over- (under-)education on firm productivity. Moreover, their results show that the effect of over-education on productivity is stronger among firms: (i) with a higher share of high-skilled jobs, (ii) belonging to high-tech/knowledge-intensive industries, and (iii) evolving in a more uncertain economic environment. Interaction effects between under-education and working environments are less clear-cut. However, economic uncertainty is systematically found to accentuate the detrimental effect of under-education on productivity.