Living Labs have become a popular approach to facilitate multi-stakeholder engagement in open innovation processes in real-life settings. Despite their extensive application across various research fields, there is still a lack of theoretical understanding in this area. This study aims to take the first step towards developing a theory for Living Labs. In doing so, we will review the current state of the art of Living Lab theories as well as identify areas where further theoretical support is required. To achieve this, grounded theory will be used as the overarching approach to rigorously review literature. The outcome of this research will be a taxonomy of Living Lab theories, classified according to the emerged themes from grounded theory analysis. Additionally, the study will identify areas where Living Lab research needs to be theorized to support both researchers and practitioners in this area.