Collaboration is often motivated by the perception of interdependence, with success in one organization deemed conditional upon the actions of another. In the public sector, interdependence typically surfaces when alleviating complex social and economic problems whose causes cut across organizational domains. Our paper, however, examines general operating costs, rather than specific policy outcomes, as an alternative interdependency motivating collaboration. This development has become more prominent arising from severe financial pressure, which has motivated many public agencies to recognize such operating-cost interdependencies and address them by pursuing ‘collaborative efficiency’ measures. Examples include shared back-office services, purchasing consortia and one-stop shops. We propose to explore these manifestations of collaborative efficiencies by considering the economies of scale, scope and learning which they seek to deliver. We also present a review of the field before considering the policy and research implications of this trend and how we might understand it.