Christiaan Gerardus Cornelissen (30 August 1864 – 21 January 1942) was a Dutch syndicalist writer, economist, and trade unionist. Cornelissen was the second of five children of Johannes Cornelissen, carpenter in Den Bosch, North Brabant, and Mechelina van Wijk. He became a primary school teacher in Middelburg, Zeeland. In the late 1880s he started working for ("Justice for All"), the organ of the Social Democratic League (in Dutch: Sociaal-Democratische Bond, SDB). Next to Ferdinand Domela Nieuwenhuis, he soon became a leader in the SDB, member of the central committee and head of the international secretariat. He stayed in the SDB, which was renamed to Socialist League, during the breakaway of the Social Democratic Workers' Party (in Dutch: Sociaal Democratische Arbeiders Partij, SDAP).