The MMC (Mobility Monitoring Centre) of Thessaloniki is operated by the Hellenic Institute of Transport of CERTH and collects, analyses and disseminates mobility related data for the city. The MMC of Thessaloniki objectives are to monitor the operation and development of the transport system of the city, integrate data from different sources, support planning and decision making, provide a platform where different actors can share and disseminate data, provide mobility information to the general public and to promote sustainable mobility, and as a result, improve quality of life in the city. In the framework of a number of European, transnational and national projects the transport systems of the city have been (and is being) equipped with ITS infrastructure collecting useful traffic data. These data, integrated with other mobility data, probe data and social content, are being managed in the Big Data infrastructure for processing, analysing and visualizing multi-source data in real time that has been installed in CERTH/HIT premises. Data analytics, advanced visualization and indicators estimation tools have been developed and a transport modelling lab has been set up. In addition, on-line services for interaction with the travellers have been developed and an open data portal providing aggregated traffic data for Thessaloniki is available.