Simon Stevin (1548-1620) was one of the leading scholars of his day. As a scientist and engineer, he carved a career for himself in the breakaway Dutch Republic of the Northern Low Countries, developing theoretical innovations in mathematics and physics as well as practical innovations in civil engineering and military technology. Less well known is the project that Stevin worked on during the last twenty years of his life, a treatise on architecture and town planning. The earliest mention of Huysbou occurs in the first volume of Stevin’s work on mathematics and other natural sciences, Wisconstighe Ghedachtenissen (‘Mathematical Memoirs’), published in 1605. This book deals with Stevin’s unfinished, and until now only partly revealed architectural treatise. The discussion of the Huysbou opens by exploring Stevin’s visions on science and methods to explain the origins of the ideas contained in the work. The following chapters examine Stevin’s notions of symmetry and order in architecture, his views on building methods, the role of water and the use of visual presentations of architecture. Finally the commentary surveys Stevin’s contribution to architectural theory and the reputation enjoyed by Huysbou in the Low Countries and in the broader European context. The second section of the book presents Stevin’s work on architecture and town planning. A first attempt has made to recreate the envisaged Huysbou as accurately as possible. The third section contains the appendices: fragments of Stevin’s texts on architecture and town planning, a glossary and an extensive bibliography.