This Recommendation outlines the key performance indicators (KPIs) in the context of smart sustainable cities (SSC). Evaluating these indicators can help cities as well as their stakeholders understand to what extent they may be perceived as smart sustainable cities (SSCs). The sustainability of a smart city is based on four main aspects: ?C Economic: The ability to generate income and employment for the livelihood of the inhabitants. ?C Social: The ability to ensure that the welfare (safety@ health@ education) of the citizens can be equally delivered despite differences in class@ race or gender. ?C Environmental: The ability to protect future quality and reproducibility of natural resources. ?C Governance: The ability to maintain social conditions of stability@ democracy@ participation and justice. This Recommendation can be utilized by: ?C Cities and municipal administrations@ including the SSC-relevant policy-making organizations@ and government sectors@ enabling them to develop strategies and understand the progress related to the use of ICT for making cities smarter and more sustainable. ?C City residents and non-profit citizen organizations@ enabling them to understand the development and progress of SSCs with respect to the impact of ICTs. ?C Development and operation organizations of SSC@ including planning units@ SSC-related producers and service providers@ operation and maintenance organizations@ helping them to fulfil the tasks of sharing information related to the use of ICT and its impact on the sustainability of cities. ?C Third party agencies and academia@ supporting them in the selection of relevant KPIs for assessing the contribution from ICTs in the development of SSCs. The intention of KPIs is to publish the criteria to evaluate ICT?s contributions in making cities smarter and more sustainable@ and to provide the cities with the means for self-assessments. It is desirable that each city can quantify continuously an achievement degree according to their goal following KPIs.