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The link between human capital and economic activity has been the subject of numerous theoretical and empirical analyses in economics and management (Schultz 1959, Becker 1993, Lucas 1988). Innovation capacity could be the main explanatory factor: highly skilled players in firms seem to have a higher propensity to innovate. Social capital, still a very polysemous notion, appears to constitute another form of intangible capital for companies. Several works, mainly in the field of human resources, have shown the importance of social climate and the organization of work in driving individual and collective performance. We argue that the link between social capital and firm performance lies in the interaction between social capital and human capital. These two factors influence each other in different ways. We will first study the different definitions given to these two forms of immaterial capital according to the authors, and analyze their associated properties. From this conceptual analysis, we will then try to determine and highlight the variety of interactions (in terms of complementarities or substitutions) between these two forms of capital, as well as the dynamics of these interactions.