Privacy & regulation · also called US v. Google ad tech case, DOJ v. Google ad tech
United States v. Google (ad tech)
United States v. Google (ad tech) is the US Justice Department's antitrust case in which a federal court ruled in April 2025 that Google illegally monopolised key open-web ad tech markets.
The DOJ and a group of states sued Google in January 2023 in the Eastern District of Virginia, alleging it had monopolised the technology publishers and advertisers use to buy and sell display ads on the open web. After a bench trial in September 2024, Judge Leonie Brinkema ruled on 17 April 2025 that Google had willfully monopolised the markets for publisher ad servers (its DFP, now part of Google Ad Manager) and ad exchanges (AdX), and had unlawfully tied the two together. The court did not find a monopoly in an advertiser ad network market.
A remedies trial followed in September 2025, where the DOJ sought divestiture of AdX. In September 2026 the court rejected the break-up and, according to reporting on the decision, ordered behavioural remedies instead, such as interoperability with Prebid and rival publisher ad servers, sharing auction data with publishers, and a technical monitor. Google has said it will appeal the liability ruling.
The case matters because it formally found that Google's control of both the publisher ad server and the ad exchange harmed competition, and its remedies will shape how open-web auctions work.
Think of it like this
The case is like a court deciding that one company should not both own the only popular auction house and run the most-used sellers' agency, then choosing house rules instead of forcing a sale.
An example
Publishers following the case watch for remedy details such as whether AdX bids will be available on equal terms to non-Google ad servers, which could change how they set up header bidding.
Related terms
Antitrust in ad tech
Antitrust in ad tech refers to competition-law cases and investigations examining whether dominant companies, especially Google, have monopolised or abused their position in the technology used to buy and sell ads.
Publisher ad server
A publisher ad server is the system a website, app or streamer uses to manage its ad inventory and decide, for every ad slot, which campaign or programmatic buyer gets the impression.
Ad exchange
An ad exchange is a digital marketplace where buyers and sellers of ad impressions meet and trade through automated auctions, usually in real time.
Prebid
Prebid is the most widely used open-source header bidding software, including Prebid.js for websites, Prebid Server for server-side auctions and Prebid Mobile for apps.
Header bidding
Header bidding is a technique where a publisher offers each ad impression to many SSPs and exchanges simultaneously before calling its ad server, so all buyers compete at once.
Sources: US DOJ: Department of Justice prevails in landmark antitrust case against Google (April 2025), US DOJ case page: U.S. and Plaintiff States v. Google LLC (2023), US DOJ: Justice Department sues Google for monopolizing digital advertising technologies (January 2023), AdExchanger: summary of the unsealed remedies decision (September 2026)