Online advertising refers primarily to the use of the Internet, and to a lesser degree, additional new media (e.g., text messaging), for the purposes of marketing and advertising goods and services to the public. It thus generally entails a relationship between websites (publishers) and advertisers who create ad content.

Online advertising is one main form of digital media, and it includes search ads, display ads, mobile ads, and video ads. Its current production is the result of an updated, Internet-oriented, advertising industry, such as that represented by the Web Marketing Association, a sponsor group for assessing web marketing standards worldwide. This entry explores the history, features, and economics of online advertising.