Nielsen Media Research (NMR) is an American firm that measures media audiences, including television, radio, theatre, films (via the AMC Theatres MAP program), and newspapers. Headquartered in New York City, it is best known for the Nielsen ratings, an audience measurement system of television viewership that for years has been the deciding factor in canceling or renewing television shows by television networks. As of August 2024, it is the primary part of Nielsen Holdings.

NMR began as a division of ACNielsen, a marketing research firm founded in 1923. In 1996, NMR was split off into an independent company, and in 1999, was purchased by the Dutch conglomerate VNU. In 2001, VNU also purchased ACNielsen, thereby bringing both companies under the same corporate umbrella for years. NMR is also a sister company to Nielsen//NetRatings, which measures Internet and digital media audiences. VNU was reorganized and renamed the Nielsen Company in 2007. NMR was separated again from the NielsenIQ (the former ACNielsen) in 2021.