SIRIUS (Strategic Initiative for the Research and Innovation in the Urban Society) is a European Union initiative that aims to develop innovative and sustainable urban solutions. It brings together over 200 leading cities, universities, research institutes, and industry partners across Europe to develop, test, and deploy innovative technologies and services in the areas of mobility, energy, circular economy, digitalisation, and smart cities. The initiative is funded by the European Commission under the Horizon 2020 programme, and is coordinated by the Joint Research Centre of the European Commission.