Kees Christiaanse (b. 1953, Amsterdam) is an architect and urban planner from the Netherlands. After working with Rem Koolhaas, he started his own firms Kees Christiaanse Architects & Planners (KCAP) in 1989 and Architects and Planners (ASTOC) in Cologne. Christiaanse worked with Rem Koolhaas' architecture firm, OMA, where he was made a partner in 1983 at the age of 30, and worked for the firm until 1989. After OMA, he founded his own two firms, Kees Christiaanse Architects and Planners (KCAP) in Rotterdam and ASTOC Architects and Planners (Cologne). He was also artistic director of the Dutch Building Department from 1993 to 1996. From 1996 to 2003 he was a professor of architecture and urban planning at the Technical University of Berlin, and is now the Chair of Architecture and Urbanism in the Institute for Urban Design at the ETH in Zurich.

Two monographs on Christiaanse's work have been published, and an exhibition of the work done by his firms, "The City as Loft," was held at De Singel in Antwerp in 2003. He now lives and works in Zurich.