D. A. Flentrop (1 May 1910, Zaandam — 30 November 2003, Santpoort-Zuid) was a Dutch master organ builder and restorer who served as a proprietor and director of Flentrop Orgelbouw from 1940 to 1976. Among hundreds of restorations and new builds that Dirk Andries Flentrop completed throughout his career, perhaps the best-known project is a major 1977 restoration of two historic organs at the Mexico City Metropolitan Cathedral. Flentrop was particularly active in North America, prompting John T. Fesperman, an organist, musicologist, and Smithsonian Institution curator, to write a book, Flentrop in America (Sunbury Press, 1982), that documented the Dutch maker's 1939–77 activities in the USA and his long-lasting impact in the Americas. In recognition of his pioneering work in classic organ building, D.A. Flentrop received Honorary Doctorates in Musicology from Oberlin College (1968) and Duke University (1976).

Flentrop initially apprenticed at the family workshop with his father, Hendrik Wichert Flentrop (1866—1950), and later received additional training at the Danish firm Frobenius Orgelbyggeri and under Paul Faust (1872—1953) in Schwelm, Germany. Since his early youth, Dirk eagerly adopted the Organ Reform Movement. Flentrop lectured at the Dutch Organist Society in 1927, strongly arguing for returning to a tracker action, Rückpositiv, slider chests, and other traditional techniques and design elements. In 1940, as his 74-year-old father retired, D.A. Flentrop took over the family business. Under his leadership, Flentrop Orgelbouw significantly expanded and set a strong presence in the United States and South America. Dirk retired in 1976, passing the family business to Johannes Hans A. Steketee (1936—2010), who had worked at Flentrop as an organ builder for over 18 years.