The objective of this paper is to comprehensively review the existing MaaS schemes and develop an index to evaluate the level of mobility integration for each MaaS scheme based on the assumption that higher level of integration is more appealing to travellers. The review presented in this paper allows a comparison among the existing schemes and provides the background and the key points of MaaS systems that the research community should take into account in designing surveys. It is also provides significant insights to transport operators and authorities on the components they should take into account to apply an attractive MaaS scheme that could potential shift demand away from private vehicles.