Urban Living Labs (ULL) are considered spaces to facilitate experimentation about sustainability solutions. ULL represent sites that allow different urban actors to design, test and learn from socio-technical innovations. However, despite their recent proliferation in the European policy sphere, the underlying processes through which ULL might be able to generate and diffuse new socio-technical configurations beyond their immediate boundaries have been largely disregarded and it remains to be examined how they contribute to urban sustainability transitions. With this study, we contribute to a better understanding of the diffusion mechanisms and strategies through which ULL (seek to) create a wider impact using the conceptual lens of transition studies. The mechanisms of diffusion are investigated in four distinct ULL in Rotterdam, the Netherlands and Malmö, Sweden. The empirical results indicate six specific strategies that aim to support the diffusion of innovations and know-how developed within ULL to a broader context: transformative place-making, activating network partners, replication of lab structure, education and training, stimulating entrepreneurial growth and narratives of impact.