Sustainability introduces new goals in building design and requires new skills and project management methods. These include environmental assessment methods, the choice and use of which often has a marked impact on the outcome. Comparing the use in practice of the French evaluation system HQE and that most often used in Britain, BREEAM, permits the identification of shared trends in these two countries but also suggests that one of the reasons for a variety of outcomes lies in the structure of these assessment methods. To some extent, these depend, too, on national traditions of development, and of governance.