This special double issue extensively features both built and unbuilt work by Álvaro Siza. The Portuguese architect has developed a large number of projects, and the relationship between the realised and the concept is central to this examination of his career. Being equally attentive to the architect’s built and unbuilt works allows a global understanding of the plurality of situations that are found in his oeuvre to emerge. The first volume features finished works like the Nadir Afonso Museum, 611 West 56th Street in New York, and the Mimesis Museum, while the second volume of numerous unbuilt works includes sketches, drawings, and plans, as well as in-depth analysis.