Posthumus (26 February 1880 in Amsterdam – 18 April 1960 in Bussum) was a Dutch economic historian, political scientist, and professor at Erasmus University Rotterdam.

In 1908 he graduated with a Doctorate of Public Sciences, writing his dissertation on the "History of the Leidsche sheet industry".

In 1915, he founded and published the Economisch-Historisch Jaarboek—a yearly collection of primary source documents and empirical analysis of Dutch merchant records.

In 1922 he was appointed as a lecturer at the Faculty of Arts and Philosophy in Amsterdam, and in 1932 he founded the Economic Historical Library.

Posthumus Instituut, a graduate research facility in economics at the University of Groningen, was founded in 1988[7] in his honor.

On 7 January 1931 Posthumus married his second wife Willemijn van der Goot, a feminist and the first Dutch woman to earn a doctorate in economics.

They had one child, Claire, in Amsterdam in 1938, shortly before moving to Noordwijk aan Zee and later Leiden for the duration of World War II.