Mobility as a Service (MaaS) is a digital concept that centres on integrating traditional public transport offerings with other types of mobility services such as carsharing and ridesourcing. In recent years, MaaS has become a much-discussed topic within the public transport industry since proponents of the concept argue that its rise will disrupt the current role of public transport authorities and increase the attractiveness of public transport. This chapter aims to give an overview of what MaaS is and what its prospective diffusion may imply for public transport authorities and public transport systems. To do so, a definition of MaaS is first provided, followed by a brief review of expectations on how MaaS will influence traditional public transport. A framework that describes different pathways to governing MaaS developments is introduced next and is subsequently used to analyse and discuss how public transport authorities in Finland, Sweden, and Norway have approached MaaS thus far. The chapter ends with some recommendations on how governments can support and shape MaaS developments based on the experience to date.