Thorikos’ theatre is the most renowned, conspicuous and controversial monument of the site. Materially and visually imposing with its peculiar, ellipsoid shape (sometimes called primitive, archaic or simply irregular), it has struck locals and travelers alike through the centuries. Archaeological exploration of the theatre began in 1886 by the American School of Classical Studies at Athens. Investigations were resumed in 1963 and 1965 by the Committee for Belgian excavations in Greece, and in 2011-12 by the Greek Archaeological Service (Ephorate of Antiquities of East Attica). During these three campaigns, the theatre was partially excavated. The seating section (cavea or koilon) is divided in two – the lower (earlier) with rows of built bench-seats, a small temple of Dionysos and an altar flanking the oblong stage (orchestra), as well as an enigmatic room with a bench. All these were erected on the surface of an earlier marble- and limestone quarry between two long-lived mines and a cemetery with conspicuous tombs from the 6th-4th centuries BC. The earliest built feature of the theatre has been dated to the first half of the 5th century BC, whereas what we see today was shaped by an extensive construction phase in the 4th century BC. Ancient theatres, especially those of the rural chóra, were inseparably linked to the sociopolitical organization of the Athenian polity, structured by Kleisthenes’ demes-and-trittyes system, in place since the late 6th century BC. Aside from accommodating the staging of dráma in the context of festivals in honour of Dionysos, theatres functioned as congregation foci for citizens contributing to the Athenian democratic institutions. At Thorikos, the capacity of the theatre is estimated to 3184–3826 seats. A new Belgian-Greek project is currently revisiting the archives and finds of all excavations to date, supplemented by small-scale, targeted excavations and applying modern techniques such as 3D-scanning and reconstruction with a view to a comprehensive publication.