Civil engineering is experiencing an increasing stakeholder emphasis on sustainable development (SD). As such, it is becoming ever more important that engineers share knowledge and information to cope with the complex integrated nature of SD. This article uses social network analysis (SNA) to explore SD knowledge and information sharing relationships. Three functional units within an international civil engineering consultancy were web surveyed to solicit population members' SD contacts, achieving a 76.8% response rate. The data was analysed with the aim of understanding: intra-population and cross-boundary connectivity; relationship effectiveness; and key players within the networks. This revealed three main findings. First, cross-functional relationships were commonplace, suggesting population members were seeking SD knowledge and information from other specialist areas. Second, population members were more likely to approach co-located peers for knowledge and information; they often exhibited fewer inter-office SD relationships - a common issue due to the inherent costs of developing and maintaining long-distance relationships. Finally, population members felt that they did not need to regularly interface with SD contacts in order to maintain good relationships; they were able to maintain a reasonable knowledge and skills awareness, gain timely access and successfully engage with the majority of actors with whom they infrequently contacted. The article concludes by emphasising how SNA can be applied in broader SD contexts to provide insight into how SD knowledge and information sharing performance can be enhanced within organisations, project teams and communities.