Audience measurement measures how many people are in an audience, usually in relation to radio listenership and television viewership, but also in relation to newspaper and magazine readership and, increasingly, web traffic on websites. Sometimes, the term is used as pertaining to practices which help broadcasters and advertisers determine who is listening rather than just how many people are listening. In some parts of the world, the resulting relative numbers are referred to as audience share, while in other places the broader term market share is used. This broader meaning is also called audience research.

Measurements are broken down by media market, which for the most part corresponds to metropolitan areas, both large and small.

The diary was one of the first methods of recording information. However, this is prone to mistakes and forgetfulness, as well as subjectivity. Data is also collected down to the level of listener opinion of individual songs, cross referenced against their age, race, and economic status in listening sessions sponsored by oldies and mix formatted stations. IBOPE was the first realtime service for audience measurement of the world, it started in São Paulo in 1988. ]\ countries.