Jef Geys (b. 1934, Léopoldsburg / Belgium, d. 2018, Genk, Belgium) was a conceptual artist, who made sculptures, installations, photographies and films. In 2002, he presented his 36 hour film "Day and Night and Day and ..." at documenta 11 in Kassel. He also participated in Skulptur Projekte Münster (1997), and the Venice Biennale (2009). Jef Geys studied at the Academy of Antwerp.