Advertising was once primarily a subsidy for news and entertainment media, such as television, magazines and newspapers. Nowadays, it’s more of a subsidy for online services and increasingly for merchants looking to boost their razor-thin operating margins.

At the same time, Chinese firms have become a much bigger part of the market. Both trends are evident from a list of the 10 biggest global ad sellers—firms that make money by selling space on their sites to advertisers—compiled by WPP’s media-buying arm for calendar year 2025 (see the above chart).