Sustainable design faces challenges at a scale and level of complexity that are ill at ease with design’s mainstream focus on products and users. Recently, social practice theory has been suggested as a promising theoretical framework to inform new ways of designing. In social practice theory, practices – socially shared entities such as cleaning, cooking and playing – are taken as the fundamental unit of analysis. So far, however, design research in this area has been scattered and varying strongly in its interpretations of the implications of a ‘practice-orientation’. This thesis explores these implications through a series of empirical projects on the topics of bathing and staying warm at home and proposes a coherent practice-oriented approach to sustainable design.