In this paper we address two interrelated research gaps in the Corporate Social Responsibility (CSR) literature. The first results from a lack of understanding of different patterns of CSR engagement with respect to CSR talk (impression management and the creation of symbolic images and documentation) and CSR walk (substantive implementation of CSR policies, structures and procedures). Related to this, the second gap concerns limited knowledge about the influence of firm size on CSR engagement. We develop a conceptual model that explains differences in CSR talk versus walk based on organizational cost and firm size. This allows us to theorize the antecedents of what we call the large firm implementation gap (large firms tend to focus on communicating CSR symbolically but do less to implement it into their core structures and procedures) and vice versa the small firm communication gap (less active communication and more emphasis on implementation). Our model expands a new theoretical understanding of CSR engagement based on as yet underemphasized firm-level antecedents of CSR, and opens up several new avenues for future, and in particular comparative, research.