Thessaloniki (Greek: Θεσσαλονίκη, IPA: [θesaloˈniki]), Thessalonica, or Salonica is the second-largest city in Greece and the capital of the Greek region of Macedonia.

It is honourably called the Συμπρωτεύουσα Symprotevousa (lit. co-capital) of Greece, as it was once called the συμβασιλεύουσα symvasilevousa (royal co-capital) of the Byzantine Empire. According to the 2001 census, the municipality of Thessaloniki had a population of 363,987. The entire Thessaloniki Urban Area had a population of 763,468.

Thessaloniki is Greece's second major economic, industrial, commercial and political centre, and a major transportation hub for the rest of southeastern Europe; its commercial port is also of great importance for Greece and its southeast European hinterland. The city hosts an annual International Trade Fair, the Thessaloniki International Film Festival, and the largest bi-annual meeting of the Greek diaspora.

Thessaloniki retains several Ottoman and Jewish structures as well as a large number of Byzantine architectural monuments.