What is a walled garden in advertising?
A walled garden is a platform that controls its own ad inventory, audience data, buying tools and measurement end to end, and keeps its data inside its own ecosystem. Google, Meta, Amazon, TikTok and Apple are the main examples. Advertisers gain scale and rich targeting, but have limited independent visibility into how their ads perform.
Walled gardens contrast with the open web, where independent publishers sell through many third-party ad tech companies. Walled gardens usually do not allow outside verification tags or share user-level data, instead offering their own reporting, lift study tools or data clean rooms.
Their share of digital ad spend has grown, a key reason for open-web ad tech consolidation. Regulators' antitrust in ad tech cases and the EU's Digital Markets Act aim partly at the power these companies hold over advertising markets.