How do you design a sustainable urban area from scratch? A growing number of urban development projects, marketing themselves as sustainable or ‘eco’ cities, claim to have the answer. This paper focuses on the companies who create the masterplans that guide the development of such sustainable urban projects. While these projects are appearing in a diverse array of locations around the world, they are largely conceived and designed by a small, elite group of international architecture, engineering and planning firms based in North America and Europe sometimes referred to as the global intelligence corps (GIC). Drawing on research into these firms, the paper examines the contemporary drivers of internationalisation in sustainable urban planning and design. These include enhanced professional reputations and satisfaction for designers and branding benefits for clients with a desire to be seen as modern and ‘global’. The paper then considers the role of international masterplanners in the global dissemination of ideas in this area, concluding that the GIC and the plans they develop are playing a significant role in the development of an international model of sustainable urbanism. However, the way in which this model is actually expressed in material form is strongly influenced by the demands and priorities of the GIC's international clients. The paper concludes by reflecting on what this research demonstrates about what it means for a planning model to be both relational and territorial.