Syntagma Square is the central square of Athens, Greece. The square is named after the Constitution that Otto, the first King of Greece, was obliged to grant after a popular and military uprising on 3 September 1843. It is located in front of the 19th-century Old Royal Palace, housing the Greek Parliament since 1934. Syntagma Square is the most important square of modern Athens from both a historical and social point of view, at the heart of commercial activity and Greek politics. The name Syntagma alone also refers to the neighbourhood surrounding the square. The metro station underneath the square, where lines 2 and 3 connect, along with the tram terminal and the numerous bus stops, constitutes one of the busiest transport hubs in the country.

Otto was a Bavarian prince who ruled as King of Greece from the establishment of the Kingdom of Greece on 27 May 1832, under the Convention of London, until he was deposed in October 1862.