The purpose of this study has been to explore how project-based organizations should structure their purchasing organization regarding the aspects of centralization and decentralization. The study has also explored how these aspects affect the purchasing process. To address this purpose, two research questions formed the basis for the study, these are:•Research question 1: Which aspects affect the degree of centralization and decentralization regarding purchasing in project-based organizations?•Research question 2: How do these aspects affect the purchasing process of a project-based organization?Different aspects has been identified through a thematic analysis and the most interesting aspects are; coordination and oversight, support and training, sharing of information and knowledge, and the scope of the purchasing organization.The result of the study shows that a purchasing organization at a project-based organization should form a mix of centralization and decentralization. A centralized purchasing function that can coordinate and support purchasing is necessary in project-based organizations. The purchasing function should also act as a gatekeeper that gather and distributes information to relevant areas of the organization. It is important that the scope of the purchasing organization does not become too extensive and that a centralized function does not gain too much control. The local knowledge that exists in the different projects is an important factor to take advantage of in the purchasing process.The study has concluded that another step in the purchasing process exists that is not described in prior theory. This step is about implementing a purchasing decision throughout the organization. The practical implication of the study regards the local knowledge that exists in the different projects and that it is important to take advantage of that knowledge.