ICOS Cities demonstrates how standardized, observation-based greenhouse gas (GHG) monitoring can enhance the effectiveness of urban climate action. Building on pilot city experiences in Munich, Paris, and Zurich, this deliverable outlines the organizational and financial plan for establishing an ICOS Calibration Cities Network (ICCN) as a long-term extension of the Integrated Carbon Observation System (ICOS). The ICCN would form a coordinated network of 8–15 representative European cities equipped with standardized urban observatories integrating high-precision reference instruments and costeffective sensor networks. Its goal is to provide reliable, observation-based verification of city-scale GHG emissions, improving the accuracy and usability of inventories that underpin local climate policies. In summary, Deliverable 6.2 defines a scalable and sustainable model for integrating urban GHG observation into European research infrastructure. The proposed ICOS Calibration Cities Network will enable standardized, science-based verification of emission reductions, strengthening the scientific foundation for urban climate neutrality under the European Green Deal.