In a context of the project-based organization's (PBO) reinforcement, the question of knowledge management has become an important issue for companies as well as for research in management. This paper focuses on highlighting and examining the mechanisms that are used to manage knowledge together with projects. Our research is based on a qualitative approach centred on a multiple case study in four PBOs operating in different sectors: IBM, Hewlett-Packard, Arkopharma, and Temex. The analysis of the four case studies enables us to identify and discuss the different mechanisms underlying knowledge management in PBOs. The paper is original because it investigates the framework of mechanisms to improve the understanding of knowledge management in PBOs.