A leadership election was held on 12 November and 19 November 2017 by the centre-left political parties of Greece, with the participation of Panhellenic Socialist Movement (PASOK), Greece's main centre-left party and The River (Potami), another parliamentary party. The Movement of Democratic Socialists (KIDISO) and the Union of Democratic National Reform movement (EDEM) also supported the elections. The first round of election was held on 12 November. No candidate gained 50% of the votes, so a runoff vote was held on 19 November. The elections were regulated by an election committee under the presidency of Nikos Alivizatos.