Nielsen is a global marketing and advertising research company headquartered in Lower Manhattan, New York City. Nielsen is active in over 100 countries, and employs some 32,000 people worldwide. Total revenues amounted to $5.1 billion in 2010.
Nielsen is a publicly held global information and media company, and is one of the world's leading suppliers of marketing information (Nielsen Consumer, formerly ACNielsen), media information and TV ratings (Nielsen Media Research), online intelligence (Nielsen Online) and mobile measurement (Nielsen Mobile). On January 25, 2011 the company issued an IPO raising $1.6 billion in the biggest private equity-backed U.S. IPO since 2006. (Source: Wikipedia)