Despite the work done to date, project sustainability management (PSM) is still at an embryonic stage. The existing literature considers sustainability as a transversal aspect to be incorporated into the traditional management functions (scope, time, cost, quality, etc.). This article proposes sustainability as a key aspect of project management, with three essential components: principles, processes and competences. Regarding principles, the principle of sustainable development should be added to those generally suggested. As for processes, seven are proposed for (1) planning sustainability management; (2) establishing a sustainability breakdown structure; (3) defining the sustainability objective; (4) identifying project alternatives to achieve it; (5) planning and (6) implementing the sustainability strategy; and (7) monitoring and control. The main interrelationships between these processes and those of project initiation, planning, implementation, control, and closure are also analysed. In addition, the competences that the project manager should have in this field are identified, as well as the main criteria to take into account in order to adapt PSM processes to the characteristics of the project and the organisation. Finally, the results of a Delphi analysis carried out to validate these proposals are presented.