Pieter Jacobus (Piet) Meertens (Middelburg, 6 September 1899 – Amstelveen, 28 October 1985) was a Dutch scholar of literature, dialects, and ethnology. He founded the institutes which later merged into the Meertens Instituut (a research institute operated by the Royal Netherlands Academy of Arts and Sciences), of which he was the director until 1965.
Meertens attended the Stedelijk Gymnasium Middelburg, and studied Dutch in Utrecht. He was promoted in 1943 with a dissertation on literary life in Zeeland in the 16th and 17th centuries, under the direction of Cornelis de Vooys.
After his studies, Meertens taught school for a few years. On 1 July 1930 he became secretary of the committee of dialects for the Royal Netherlands Academy of Arts and Sciences (KNAW); starting with only two assistants he built a system of documentation that employed two thousands correspondents throughout the country who reported on local dialects. In 1934 the KNAW started a committee for ethnology, and Meertens presided over that committee as well, laying the foundation for the institute which was to receive his name in 1979.
He was actively involved with the Phonologische Werkgemeenschap, an organization of phonologists, and when the Centrale Commissie voor Onderzoek naar het Nederlandse Volkseigen was founded in 1948, a state-supported institution that oversaw the entire field of Dutch linguistics and onomastics, Meertens was appointed president of the bureaus for dialectology, onomastics, and ethnography, a function he held until his retirement in 1965. In 1950 he was one of the founders of the Algemene Vereniging voor Taalwetenschap (AVT), the General Organization for Linguistics.
In 1966 he became member of the Royal Netherlands Academy for Arts and Sciences.
Meertens was a progressive Christian, and a member of the small Christian Democratic Union. In the 1920s, when in Utrecht, he was a member of the board of the Dutch Association of Vegetarians. He was sympathetic to the anti-militaristic strain in the Dutch Reformed Church, and visited prisoners as part of a missionary organization. Christian-Socialist friends of his were journalist Henk van Randwijk, preachers Willem Banning en Jan Buskes, and poet Fedde Schurer. From 1938 on he was active in the Comité van Waakzaamheid, an association of artists and intellectuals inspired by Menno ter Braak which opposed the rise of fascism and nazism.