Nielsen Media Research (NMR) is an American firm that measures media audiences, including television, radio, theatre films (via the AMC MAP program ) and newspapers. NMR, headquartered in New York City and operating primarily from Oldsmar, Florida, is best-known for the Nielsen Ratings, a measurement of television viewership.

Nielsen Media Research began as a division of ACNielsen, a marketing research firm. In 1996, Nielsen Media Research 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. VNU was reorganized and renamed the Nielsen Company in 2007.

The Nielsen TV Ratings have been produced since the 1950s and statistically measure which programs are watched by different segments of the population. The most well known portion is the "diary". During the 4 sweeps months of February, May, July and November, Nielsen interviewers in Dunedin, Florida and Radcliff, Kentucky ask homes to participate in filling out a diary of the programs watched in their home for a one week period. Nielsen has ways of measuring American TV viewing other than the diaries. Recently, Nielsen announced the launch of its A2M2 project that would measure television viewing in and out of the home.

Nielsen Media Research is a sister company to Nielsen//NetRatings, which measures Internet and digital media audiences through a telephone and internet survey, and Nielsen BuzzMetrics, which measures Consumer-Generated Media.

Nielsen also conducts market research for the film industry through National Research Group (NRG). http://www.nrg.com/

Nielsen recently purchased Telefia - a mobile metrics marketing research firm. [citation needed]