(Bloomberg)—WPP Plc, the world’s largest advertising company, agreed to buy closely held e-commerce specialist Triad Retail Media LLC to extend its reach into online shopping.

WPP is buying St. Petersburg, Florida-based Triad through its media and advertising technology company Xaxis, according to a statement Thursday. Terms of the deal weren’t disclosed.

Triad, which counts retail giants Wal-Mart Stores Inc., No. 4 in the Internet Retailer 2016 Top 500 Guide, Toys R Us Inc. (No. 35) and online marketplace eBay Inc. as clients, had net revenue of more than $120 million last year, gross revenues exceeding $500 million and about 700 employees, according to the statement. The company lets retailers advertise to online shoppers while they’re browsing and making purchases on mobile phones and websites.

The deal is among more than two dozen purchases for London-based WPP this year as the advertising, marketing and communications giant continues to expand. WPP founder and CEO Martin Sorrell bought shopping-basket maker Wire & Plastics Products Plc three decades ago and used it to build an advertising conglomerate that today operates in more than 100 countries.