Crimson Historians & Urbanists (formerly known as Crimson Architectural Historians) is a group of architectural historians and urbanists based in Rotterdam, The Netherlands. The collective was formed in 1994 when Crimson became part of the planning team for the extension of Utrecht Leidse Rijn. In the following years, the office has developed a hybrid practice that takes the contemporary city as its object. Crimson designs for the city, researches it, writes texts and books about it, shows it in exhibitions and works of art, teaches about it, gives advice on it and makes policies for it.