This Recommendation ITU-T L.1600 gives a general guidance to cities and provide an overview of key performance indicators (KPIs) in the context of smart sustainable cities (SSCs). This Recommendation is one of series of the Recommendations and Supplements which define KPIs. The series of KPI definitions documents also include: " Recommendation on key performance indicators (KPIs) related to the use of information and communication technology (ICT) in smart sustainable cities [ITU-T L.KPIs-SSC-ICT]. This Recommendation lists the KPIs focusing on ICT use in SSCs. " Recommendation on key performance indicators (KPIs) related to the sustainability impacts of information and communication technology (ICT) in smart sustainable cities [ITU-T L.KPIs-SSC-impact]. This Recommendation lists the KPIs proposed for ICT impact on sustainability. " Supplement on key performance indicators (KPIs) for smart sustainable cities [ITU-T L.KPIs-SSC-Supp]. This document provides information regarding KPIs and evaluation index systems of smart cities, KPIs of sustainable cities, etc.