Outdoor (or out-of-home) advertising is one of the oldest and most often overlooked forms of advertising. While it can often be thought of merely as billboards, it also encompasses venue-specific advertising, such as at sporting arenas and inside malls, on transit (e.g., the outside of a bus, on the inside of a subway system, or in an airport), and on street furniture (e.g., bus shelters, benches). This entry provides an overview of outdoor advertising, including the different types frequently used, then explores the advantages of outdoor advertising, as well as how audiences of outdoor advertising are measured.