The existing analysis of heterogeneous social responsibility in small and medium enterprises has considered the effects of individual factors. However, no holistic analysis has been performed on how different factors of heterogeneity interact and how they collectively affect SR in SMEs. Here, we propose a new systemic approach—employing the social capital concept—with the aim of identifying how and why SR is built diversely in SMEs. In particular, we focus on a positive and holistic perspective that integrates the factors proposed in (...) the literature into the social capital construct. Through a case study of four Spanish SMEs, this article proposes a systemic approach to the study of heterogeneous SR in SMEs. (shrink)