ABSTRACTUrban experiments, living labs and testbeds have emerged as influential approaches to governing cities around the world. Experimental governance allows stakeholders to trial possible futures and to embrace creativity and innovation in the pursuit of sustainability goals. Experiments are often conducted through triple helix partnerships that favour informal and distributed actions. This is a significant departure from traditional urban development processes that are informed by well-defined processes executed by public authorities to ensure the public good and are legitimated by citizens. In this paper, we investigate this tension between experimental governance and public sector legitimacy by focusing on experimental practices in two Swedish municipalities, Stockholm and Gothenburg. We gathered data through a desk-based study, participant observations and semi-structured interviews with municipal actors to investigate the input, throughput and output legitimacy of municipalities in experimental governance. The findings indicate that municipalities emphasise actions and results from experiments, while de-emphasising reflection and attention to democratic procedures and protection of the public good. The focus on legitimacy reveals the fragmented and instrumental practices of experimental governance and a deficit in organizational capacity with potential detrimental impacts on legitimacy.