Thessaloniki is one of the regional units of Greece. It is part of the Region of Central Macedonia and its capital is the city of Thessaloniki.

Thessaloniki, also known as Thessalonica, Saloniki, Salonika, or Salonica, is the second-largest city in Greece, with slightly over one million inhabitants in its metropolitan area, and the capital of the geographic region of Macedonia, the administrative region of Central Macedonia and the Decentralized Administration of Macedonia and Thrace. It is also known in Greek as "η Συμπρωτεύουσα", literally "the co-capital", a reference to its historical status as the Συμβασιλεύουσα or "co-reigning" city of the Byzantine Empire alongside Constantinople.