Supplement 17 to ITU-T L-series Recommendations provides a definition for smart sustainable city(SSC).It was developed by the Focus Group on Smart sustainable Cities (FG-SSC) that carried out an analysis of definitions for smart sustainable cities (see Technical Report "ITU-T TR SSC Def") following the adoption of the UN General Assembly 66 Resolution 288 (see "UN Resolution 288").This Supplement has been developed with input from UNECE,UNFCCC,UNESCO,UN-Habitat,other UN agencies and stakeholders.