The "belt 20-40" is the part of Amsterdam built in the period 1920-1940. Sandwiched between the ring of canals and the post-World War II urban expansions, this belt is special because of its urban design and the great attention paid to architectural details. In order to preserve as many of these special features as possible during the now necessary renovations, the municipality took special measures in the 1980s. The author is a restoration architect and has carried out several projects in the "belt 20-40". He describes, after a brief sketch of the period, which elements make this architecture so special and, in the second part of the book, how an attempt was made to restore these elements in such a way that they affect the image of the architecture as little as possible.