In the latter capacity he was influential in organizing a national and international network of libraries and their interlibrary loan operations.

Son of Hendrik Emilius August Molhuysen, director of the Deventer Stoomboot Maatschappij,[b] and Henriena Johanna Elisabeth de Lange.

Married on 12 June 1902 to Johanna Agatha Valken, and after her death in 1919, to Elsa Rachel Oppenheim on 5 August 1920, which marriage was dissolved by divorce on 8 February 1923.

On 4 November 1896 he obtained his doctorate with a thesis entitled De tribus Homeri Odysseae codicibus antiquissimis for which he had worked for quite some time in Italian libraries.

He started with the accurate description of the manuscripts, of which three volumes of Codices manuscripti Bibliothecae Universitatis Leidensis (1913) were the result.

He also laid the foundations for his edition of the Letters of Hugo Grotius, the first two parts of which were published from 1928 to 1936 in the Rijks Geschiedkundige Publicatiën series.

The National Advisory Committee on Library Services, set up by the government in 1922 on his proposal, can also be regarded as an expression of the same aim.

The aim of the commission, in addition to issuing advice to authorities, was also to promote contact between the directors of the major libraries.

In 1909, one year after the foundation of the Central Association for Public Reading Rooms, he was elected to the board, of which he served continuously until his death.

With EA van Beresteyn and HE Greve, he left his mark on the development of public libraries in our country.