The Thessaloniki Metro (Greek: Μετρό Θεσσαλονίκης, Metró Thessaloníkis, [meˈtro θesaloˈnicis]) is an underground rapid-transit system under construction in Thessaloniki, Greece's second largest city. Estimates for the cost of the megaproject are €1.62 billion ($1.83 billion) for the main line and €640 million ($723 million) for the Kalamaria extension, for a total of €2.26 billion ($2.55 billion). The project is primarily funded with loans from the European Investment Bank (EIB) and the European Regional Development Fund (ERDF) and funds from the Greek government. Construction by a Greek-Italian consortium is overseen by Attiko Metro S.A., the Greek state-owned company which oversaw construction of the Athens Metro and Athens Tram.

Proposed during the 1910s and first seriously planned in the 1980s, construction of the main line began in 2006 and on the Kalamaria extension in 2013. Although the initial proposal included three extensions to the main line, the latest Attiko Metro proposal seeks to combine the two westward extensions as a loop; the system will be made up of the main line and the Kalamaria and Evosmos extensions. The system under construction has 18 stations and 14.4 km (8.9 mi) of tunnels. Detailed planning of the airport extension went to tender in March 2019, while the Western loop went to tender in August of the same year.

After years of delays, due mainly to archaeological discoveries in the city centre during construction and in part to the Greek financial crisis, the main line is scheduled to open in 2024. The system will be entirely driverless and remote-controlled.