 He was the first exhibition organizer to specialize in dealing with conceptual art, holding group exhibitions that had no existence outside of the catalogue., and was an active "independent curator", organizing 21 art exhibitions, books, catalogues and projects, throughout the USA, Canada and Europe between February 1968 and July 1971 in a wide range of new and original formats, including several important group shows, such as "The Xeroxbook" in December 1968, and "January 5–31, 1969" exhibition, which contained no objects, no paintings and no sculptures.He was also the originator and author, with lawyer Robert Projansky, of "The Artist's Reserved Rights Transfer and Sale Agreement," published in 1971, which has been translated and published in French, Italian, German and Dutch.At the turn of the 21st century he founded the Stichting Egress Foundation in Amsterdam to bring together his varied range of projects