This Recommendation contains a maturity model for smart sustainable cities. This maturity model helps identify the goals, levels and key measures that are recommended for cities to effectively examine their current situation and determine critical capabilities needed to progress toward the long-term goal of becoming SSCs. The Recommendation includes: - Smart Sustainable City Maturity Model (SSC-MM), - maturity dimensions in smart sustainable cities, - maturity levels for smart sustainable cities, and - mapping of key performance indicators in smart sustainable cities.