The purpose of this study is to gain an understanding of how managers practise sustainability as they go about the management of organisations. Based on the Brundtland Commission's definition of sustainable development, sustainability is presented as consisting of economic prosperity, environmental quality, and social equity dimensions, commonly known as the triple bottom line. The natural resourcebased view of the firm that concentrates on the environment, is an alternative model used in the literature. Organisations and the natural environment literature uses these models to frame a research agenda, resulting in it becoming, almost by default, sustainability's 'big' theory. Despite 25 years of research in this field, prior research has failed to investigate the routine sustainability activities managers include in their everyday work to identify the ways managers understand and practise sustainability. Using components of Schatzki's practice theory, in combination with phenomenography, this study investigates the activities, understandings, and ways managers practise sustainability in the unique setting of restaurants. Data collection and analysis involves two phases. The first phase comprises of twenty-five in-depth semi-structured interviews with chefs and managers from the restaurant industry. The second phase, involves conducting observations at seven restaurants, selected from the original interview participants. These interviews and observations combined with field notes provide a unique perspective on the ways managers practise sustainability. A Practice Theoretical Account of Managers' Practice of Sustainability reveals that managers' practise and understand sustainability in five distinctly different ways. In addition, the practice theoretical account has four defining features. First, the manager's understanding of sustainability informs and organises sustainability activities to form these five distinct ways of practising sustainability. This is counter to the majority of previous frameworks, which assume there is only one way to practise sustainability. These five ways of practising sustainability are 1) Purposeful Frugality, 2) Ethical Provenance, 3) Meaningful Relationships, 4) Bio-Physical Systems, and 5) Leading Lights. Second, everyday activities of the practice of sustainability can be arranged into four key sets of sustainability activities consisting of managing business affairs, managing materiality, managing people, and managing waste. Third, there is an entwining between the activities and understanding which informs the practice of sustainability. Finally, the ways of practising sustainability exhibit a hierarchical ordering from Purposeful Frugality to Leading Lights. Understandings higher in the hierarchy comprehend complex relationships between the different key sets of sustainability activities, the inclusion of different everyday activities, and the organising of these everyday activities. By using practice theory to investigate how managers incorporate sustainability into their eve...