Advertising, a form of commercial mass communication designed to promote the sale of a product or service, or a message on behalf of an institution, organization, or candidate for political office. Evidence of advertising can be found in cultures that existed thousands of years ago, but advertising only became a major industry in the 20th century. Today the industry employs hundreds of thousands of people and influences the behavior and buying habits of billions of people. Advertising spending worldwide now exceeds $350 billion per year.