Out-of-home advertising (OOH advertising or OOH ERP) or out-of-home media (aka OOH media or outdoor media) is advertising that reaches the consumers while they are outside their homes.

Out-of-home advertising is focused on marketing to consumers when they are "on the go" in public places, in transit, waiting (such as in a medical office), and/or in specific commercial locations (such as in a retail venue). OOH advertising formats fall into four main categories: billboards, street furniture, transit, and alternative.

The OOH advertising industry in the United States includes more than 2,100 operators in 50 states representing the major out of home format categories. These OOH media companies range from public, multinational media corporations to small, independent, family-owned businesses. Currently, the United Kingdom and France are Western Europe's first and second largest markets for OOH, respectively. Data from Outsmart (formerly the Outdoor Media Centre), the UK’s out-of-home advertising trade association, shows that DOOH grew at a 29.7% CAGR from 2009 to 2014.

Billboard advertising is a traditional OOH advertising format, but there has been significant growth in digital OOH (digital billboards and place-based networks) in recent years; for example, about 4,900 digital billboard displays have been installed in China and the United States.