As new Mobility as a Service (MaaS) platforms are being established in Europe, researchers and practitioners seek evidence on the barriers experienced by the MaaS providers in their evolving business ecosystem. This paper conceptualises the MaaS business ecosystem using a Systematic Literature Review (SLR) combined with Actor- Network Theory (ANT) by constructing an actor-network of key actors. This actor- network, along with the identified MaaS business ecosystem barriers, is then used for Multiple Case Study Research, interviewing 18 European MaaS experts. The cross-case analysis revealed how MaaS providers problematise, interest, enrol and mobilise their business ecosystems. Furthermore, the paper outlines and amends key barriers in the areas of (1) technology and data, (2) social and cultural, and (3) policy and regulation. Researchers and practitioners can use the findings of this study to formulate policies, create best practices or conduct further research on the development of MaaS.