The N.W. Posthumus Institute is the Research School for Economic and Social History in the Netherlands and Flanders, including research focusing on non-Western history, world history and social-cultural history. The Posthumus Institute promotes innovative and advanced interdisciplinary research in economic and social history by stimulating joint research programs of participating institutes and provides a PhD training in economic and social history.

The Posthumus Institute is named after Prof.dr. Nicolaas Wilhelmus Posthumus (1880-1960), the first professor to hold a chair in economic history in the Netherlands. The Institute was founded in 1988 as an interuniversity training program for Dutch PhD students. In 1994, the collaborating universities decided to turn the existing organization into an Interuniversity Research Institute. In the same year the Royal Netherlands Academy of Arts and Sciences (KNAW) accredited the Institute formally as Research School for a period of five years. Most Flemish universities joined the Posthumus Institute in 2002.

The Institute for History of Leiden University houses the administrative office of the N.W. Posthumus Institute since January 1st, 2010. At this moment, fifteen faculties cooperate in the Posthumus Institute: three Belgian faculties, ten Dutch faculties, the International Institute of Social History in Amsterdam and the Centre of Social History of Limburg in Maastricht.