By 1957 Van Hoeydonck had established an international reputation. He was a member of the 'Zero' group and was a driving force behind the historic exhibition G58 Hessenhuis 'Vision in Motion, Motion in Vision' in 1959, featuring alongside Yves Klein, Heinz Mack, Daniel Spoerri, Jean Tinguely and Soto. From a concretely constructed abstraction of reality, purely geometrical structures took form during the 1950s, as displayed in a series of abstract geometrical collages and paintings. Movement and light-intervention gradually led him from spatial sensibility to space art during the early 1960s. In 1971 the crew of Apollo 15 placed Van Hoeydonck's Fallen Astronaut on the moon surface, an opportunity granted to the artist that still remains unique today.
Van Hoeydonck's oeuvre and contribution to the Belgian avant-garde is truly monumental. His rich mind, distinctive sensitivity, and innate intelligence still informs his unique expression today.
Van Hoeydonck's work is represented in many public and private collections around the world, including The Israel Museum, Jerusalem, Museum Boymans-Van Beuningen, Rotterdam, Museum of Contemporary Art, Houston, Museum of Modern Art, New York, Smithsonian Institute, Washington DC, Solomon R. Guggenheim Museum, New York, Walraff-Richartz Museum, Cologne.