A circular economy has gained attention as a potential solution to the tension between the increasing demand for and the limited supply of materials. The construction industry consumes a great amount of global resources and generates a great amount of waste, and can contribute to the shift towards a circular economy by means of a more circular building stock. In theory, modular building can contribute to a circular building stock, by securing the future utility of the stock. Multi-configuration modular building allows for adjustment and relocation of the building and deconstruction and reuse of its piece parts. Based on a collective cases study of five suppliers of modular building, the degree to which modular building can contribute to a circular economy depend on the reason for, the interpretation of and the operationalisation of modular building.