This article provides first evidence on whether corporate social responsibility (CSR) influences the productivity effects of overeducation. By relying on detailed Belgian linked employer-employee panel data covering the period 1999-2010, our empirical results exhibit a positive and significant impact of over-education on firm productivity. Moreover, they suggest that the effect of over-education is positively enhanced when the firm implements a corporate social responsibility process,

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... when it aims to have: i) a good match between job requirements and workers' educational level, ii) a diverse workforce in terms of gender and age, and iii) a long-term relationship with its workers. When focussing on required and over-education, the results suggest that CSR, besides representing an innovative and proactive approach for the firms' stakeholders, may also be beneficial for the firm itself through a bigger increase in productivity for each additional year of required or over-education. This article provides first evidence on whether corporate social responsibility (CSR) influences the productivity effects of overeducation. By relying on detailed Belgian linked employer-employee panel data covering the period 1999-2010, our empirical results exhibit a positive and significant impact of over-education on firm productivity. Moreover, they suggest that the effect of over-education is positively enhanced when the firm implements a corporate social responsibility process, especially when it aims to have: i) a good match between job requirements and workers' educational level, ii) a diverse workforce in terms of gender and age, and iii) a long-term relationship with its workers. When focussing on required and over-education, the results suggest that CSR, besides representing an innovative and proactive approach for the firms' stakeholders, may also be beneficial for the firm itself through a bigger increase in productivity for each additional year of required or overeducation. 3 for job satisfaction investigations, empirical results show that satisfaction is only correlated with job performance at a 30% level (Judge et al., 2001) . It is thus quite misleading to focus only on job satisfaction to evaluate the productivity effects of educational mismatch. However, the main methodological shortcoming of those studies is that they do not address the effect of educational mismatch on productivity directly, but always indirectly. As Hartog (2000) explains, it would be interesting to know the direct effect of over-education on productivity, rather than their indirect effects through wages, job satisfaction, and other correlates. To our knowledge, Kampelmann and Rycx (2012) and Grunau (2015) are the first to settle the basis of a direct investigation of the impact of educational mismatch on firm productivity. However, their conclusions let the door open for other developments. For example, it would be interesting to investigate whether specific firm decisions may influence the previously documented productivity implications. The contribution of this paper is to provide first evidence on whether the impact of the worker's level of education on firm productivity varies according to the firm's voluntary approach to implement a CSR process. More precisely, the ISO 26000, by defining six CSR dimensions, one of which concerning the relations with workers and their working conditions, provides guidance to firms that implement a CSR approach. The originality of this paper lies in the fact that we investigate how this dimension of CSR, measured through three different indicators, may influence the relationship between over-education and firm productivity, considering that such policies are supposed to create a specific working environment that aims at enhancing workers' productivity (McGuire, Sundgren and Schneeweis, 1988; Daubas-Bonnechère, 2008). In order to address these issues, we use an econometric specification linking over-education and firm productivity at the firm level, and consider the average firmlevel value added per worker as dependent variable. We thus estimate how mean years of over-education within firms affects the productivity of these firms (conditional on mean years of required education) in the whole private sector and according to the socially responsible policy of the firm. Our dataset allows us to control for a large range of worker and firm characteristics, which enables us to address important methodological issues such as firmlevel time-invariant heterogeneity, endogeneity, and dynamics in the adjustment process of productivity. To do so, we rely on the dynamic system GMM estimator developed by Arrelano and Bover (1995) and Blundell and Bond (1998) . The rest of this paper is organised as follows. In Section 2, we review the literature. In Sections 3 and 4, we respectively detail our methodology and dataset. We then present our results in Section 5. Finally, we discuss our results and conclude in the last section. II. Literature review Educational mismatch and productivity Considering the impact of educational mismatch on firm productivity, two different approaches can be found in the microeconometric literature. The first trend of research is based on human capital theory (Becker, 1964) , according to which education allows to develop capabilities that make workers more productive. Gaps between workers' earnings