Rietveld broke with 'De Stijl' in 1928 and became associated with a more functionalist style of architecture, known as Nieuwe Zakelijkheid The same year he joined the Congrès Internationaux d'Architecture Moderne. He designed the "Zig-Zag" chair in 1934 and started the design of the Van Gogh Museum in Amsterdam, which was finished after his death. He built hundreds of homes, many of them in the city of Utrecht. His work was neglected when rationalism came into vogue, but he later benefited from a revival of the style of the 1920s thirty years later.
His most famous design is probably the Red Blue chair, or the Zig Zag chair. Both chairs are reproduced today, and are available through Cassina.