The Hendrick de Keyser Association is committed to preserving architecturally or historically important buildings and their interiors. Buildings taken care of by 'Hendrick de Keyser' meet strict requirements. They must be striking examples of the architecture or the living culture of a certain period. History must not only be readable from the outside, but also from the inside. A lot of attention is therefore paid to building historical constructions and the quality of the interior. The collection, which grows by an average of five to ten buildings per year, includes 421 properties and complexes, including houses, farms, country estates, courtyards, villas, fishermen's houses and town halls, spread over 108 locations throughout the Netherlands. In 2018, the Hendrick de Keyser Association opened a Museum House on the Binnenluiendijk in Hoorn. This 17th-century merchant house is part of a chain of Museum houses in which visitors can experience 500 years of Dutch residential history.