For successful project management, it is essential to adopt a suitable project management approach. This approach must be based on a thorough understanding of the project characteristics in its context. In this paper we present a diagnostic model that aims to advance this understanding. We distinguish three project aspects, namely the project content, the internal context and the external context. Each of these aspects is assessed from two dimensions, namely the degree of complexity and the degree of predictability. Based on these dimensions, four project profiles can be derived: 1) design projects, 2) negotiation and expertise projects, 3) development projects and 4) negotiation, expertise and development projects. This diagnostic model aims to enhance a dialogue among key players about the approach to be followed with regard to the content and context of the project during the planning, execution and evaluation of major projects. The model can also be used as a lens to identify project risks and to propose mitigating actions.