Nielsen measures and analyzes what consumers watch and how it impacts what they buy — locally as well as globally. To help clients understand what consumers watch, Nielsen provides viewership data and analytics across television, online, and mobile screens. Clients use this information to understand their audiences, establish the value of their advertising inventory and maximize the value of their content, and to plan and optimize their spending. Nielsen ratings are the primary metrics used to determine the value of programming and advertising in the U.S. total television advertising marketplace. In addition to the United States, Nielsen measures television viewing in 29 countries. Nielsen keeps track of markets that account for approximately 80 percent of global Internet users and offers mobile measurement services in 10 countries, including the United States.