He maintained a 19th-century library specialising in the history of art. For a long time, this library was on loan to the Institute of Art History, part of the University of Amsterdam. At present, all his books have come ‘home’ and his collection has been divided between Museum Willet-Holthuysen and the Collection Centre of the Amsterdam Museum. The library will be restored to its former glory in the autumn of 2016, after which the museum collection will feature many more books.
Museum Willet-Holthuysen is managed by the Amsterdam Museum. Thanks to Louisa Willet-Holthuysen's will (1895), the City of Amsterdam has had control of this significant private 19th-century collection for more than 120 years. A large part of it is on display in the museum in the original historical setting.