The concept of corporate social responsibility (CSR) has been widely investigated, but a generally accepted theoretical framework does not yet exist. This paper argues that the idiosyncrasies of large firms and SMEs explains the different approaches to CSR, and that the notion of social capital is a more useful way of understanding the CSR approach of SMEs, whereas stakeholder theory more closely addresses the CSR approach of large firms. Based on the extant literature, we present a comparison of large firm and SME idiosyncrasies suggesting that both consolidated and emerging strategic orientations toward responsible behaviours exist. Idiosyncrasies of large firms and SMEs are also discussed to provide an assessment of the firm’s strategic CSR orientation, suggesting the key drivers upon which CSR strategies must be based. A twofold consideration emerges. First, the CSR–SME relationship could be better explained if the notion of social capital is taken into account, but this should also be accompanied by a stakeholder view of the SME; second, social capital and stakeholder theory should be taken as alternative ways of explaining CSR in both large firms and SMEs.