Most research in design project management support systems treats the subject as an isolated objective problem. The goals to be met are defined in terms of a supposed universal view of the project, and now outside concerns are taken into account. While such approaches, including project simulation, may yield excellent results, they ignore what, for many projects, are the real difficulties. Design projects are not isolated. All participants have other obligations that compete with the given project for attention and resources. The various participants in the design process have different goals. For these reasons it is proposed that design project management can be best facilitated by tools which assist the participating actors to share suitable management Information in order to make better co-ordination possible, while allowing the resource balancing between projects to occur in private. Such a tool represents the design project management task as a negotiation task that spans both projects and firms; the management of one project is the management of all. The model of design collaboration upon which the Design Coordination System (DeCo) is built was developed from 1) a heuristic case study used to gain insight into the ways in which designers co-ordinate their efforts, and 2) the application of the theory of the social contract as developed by John Rawls to the problem of design project management. The key innovation in the DeCo system is the shaping of the project management system around existing practices of collaborative project design management and planning. DeCo takes advantage of how designers already co-ordinate their work with each other and resolve disputes over deadlines and time lines. The advantage of DeCo is that it formalises these existing practices in order to accommodate both the increasing co-ordination burden and the difficulties brought about by the internationalisation of design practice. DeCo, the design project management system proposed here, provides a representation, a communications protocol, and a game theoretical decision structure. The combination of these three units provides users with the ability to exchange structured pictures of the project as seen from the points of view of individual actors. Further, it suggests a mechanism based on a specific principle of fairness for arriving at mutually acceptable project plans. The DeCo system permits the users freedom to manage their design processes as they will, while providing a basic compatibility between practices of design team members which supports their collaborative efforts to co-ordinate their design work.