Mobility as a Service (MaaS) developments have thus far progressed along different trajectories in Sweden and Finland, two pioneering countries in MaaS. Still, little is known about why this is. Addressing this knowledge gap, we investigate the role of institutions as key structures given their capacity to bring about differentiated outcomes. Based on 31 interviews with key stakeholders, we first describe drivers and barriers of MaaS developments in the two countries. Thereafter, through an analysis of similarities and differences across the cases, we identify a set of general implications for MaaS policymakers and practitioners. Developments in Finland demonstrate the importance of top-level support, of inter-organizational collaboration and of trust among key stakeholders. The Swedish case reiterates the need for inter-sectorial collaboration, particularly with regard to creating the right conditions for commercialization, and to involving stakeholders on both strategic and operational levels of the transport sector in developing the vision for MaaS. Lastly, we assess the utility of the applied theoretical framework, and comment on the necessity of recognizing that both practice-based and structural changes are needed in order to facilitate institutional change.