This paper argues that within the context of the building sector, inter-organizational relationships are determinants of innovation. To explain the workings of these relationships and their dialectical nature, an evolutionary social learning model is proposed that draws on Vygotsky's (1978) developmental psychology, Bourdieu's (1977) concept of habitus, and Wittgenstein's (1958) insights. A case study of the development of a tool designed to make builders select more sustainable building materials is analyzed to illustrate how the social learning model developed here allows an understanding of innovation. The “EcoSelector” was the tool developed to guide the builders in their selection of materials. The model provides managerial and behavioral insights into groups or individuals seeking to implement innovations in general, and sustainability innovations in particular.