Nielsen keeps tabs on what people are buying and watching. The world's #1 market research firm, Nielsen monitors consumer habits in the retail and media arenas around the globe on behalf of its customers, which include leading retailers and makers of consumer packaged goods. Active in more than 100 countries, its major business segments include retail measurement services (providing insights on such activities as distribution, pricing, merchandising, and promotion), household consumer panels (monitoring shopper behavior in about 240,000 households), and media measurement giant Nielsen Media Research.