Architect Joop van Stigt (1934-2011) has left an unconventional and original oeuvre characterized by three phases that influenced and reinforced each other. In the first twenty-five years of his work, he designed buildings and residential neighborhoods, which are interred as products of the architectural movement of structuralism. From 1980, together with his son André van Stigt, he focused on the reallocation and transformation of existing buildings. His great specialty in this field led to his appointment in 1987 as professor of Renovation and Maintenance Techniques at Delft University of Technology. After retiring in 1999, he began his third career, in Mali, Africa. There, Van Stigt trained masons and built schools and a provincial house. In all three phases he was innovative and successful; the three "careers" should not be seen as breaks in which he constantly reinvented himself, but as the three pillars of his oeuvre that continuously alternated and influenced each other.~This book focuses on the first phase of his career - his development as an architect and his oeuvre up to the early 1980s. His constructive contribution to the structuralists' theme of developing a three-dimensional modular building system is of great significance as a design methodology. His oeuvre showed how his system repeatedly gave rise to new configurations, choice of materials and arrangement of spaces, but remained constant in its proportionality. In its ingenuity and topicality, it has lost none of its power and can be of value for today's transformation tasks.~Van Stigt's mission was to provide an answer to the appeal that Van Tijen formulated in 1961 as follows: 'I also hope and expect that modern building will once again become so free in its design, that it will be able to follow every human need in all its twists and transitions and that it will overcome its rigidities, as modern furniture has done.'