Ad Exchange

An ad exchange is an electronic marketplace where individual ad impressions on websites and apps are auctioned automatically between sellers (publishers) and buyers (advertisers). Each auction starts and ends while the page or app is still loading.

What is an ad exchange?

Picture a stock exchange where the thing being traded is a single impression. On the sell side, news sites, blogs and game apps put their unsold ad slots on the exchange, usually through an SSP. On the buy side, advertisers and agencies bid through a DSP. The exchange sits in the middle: it takes the request, sends details about the impression to buyers, collects their bids and picks the winner.

The best-known example is Google Ad Exchange (AdX), which now lives inside Google Ad Manager. In Ad Manager, the “Ad Exchange” line item type is used to target open inventory for Authorized Buyers and Open Auction (Google Ad Manager Help, Ad Exchange, accessed October 2026).

How does an ad exchange work?

1. A user opens a news article that has an empty banner slot.
2. The publisher’s system sends a bid request to the exchange, along with the slot size, device type, page context and other signals.
3. The exchange passes the request to DSPs. Each DSP decides whether to bid and how much.
4. The highest valid bid wins, and the winner’s ad appears on screen.

The whole sequence runs on RTB and takes very little time. Google waits 80 to 1,000 milliseconds for buyers to respond, depending on the ad format and auction type. A response that arrives after the deadline is dropped from the auction (Google Authorized Buyers, Real-time Bidding, accessed October 2026).

How is an ad exchange different from an ad network?

What changed in 2025 and 2026: the Google ad tech case

On April 17, 2025, the U.S. federal court for the Eastern District of Virginia ruled that Google broke antitrust law by monopolizing digital advertising markets on the open web (U.S. Department of Justice, press release, April 2025).

The remedies decision followed in September 2026. The court had found that AdX and DFP, Google’s ad management tool for publishers, were unlawfully tied. Even so, Judge Leonie Brinkema did not order Google to sell AdX and chose behavioral remedies instead. Publishers using DFP no longer have to use AdX to reach Google’s demand. DFP has to work with other exchanges, Prebid included, on the same terms as AdX. A court-appointed monitor will oversee the arrangement, and the remedies last six years rather than the 15 years the plaintiffs asked for. The final judgment has not been issued yet (Tech Policy Press, September 2026). Most of the changes land on the publisher and exchange side.

What should advertisers check when buying through an exchange?

• ads.txt and app-ads.txt: files a publisher places on its domain to declare who is authorized to sell its ad inventory, which helps buyers avoid spoofed inventory (IAB Tech Lab, updated September 2026).
• sellers.json: shows the identity of the final seller and of every intermediary in the chain (IAB Tech Lab, updated October 2026).
• Placement reports by domain or app, which you use to build block lists and preferred lists.

Frequently asked questions

Can a small business buy on an ad exchange directly?

Usually not. Exchanges only accept buyers with automated bidding technology, such as DSPs or approved bidders, so small businesses tend to buy through a self-serve DSP or an agency.

Is an ad exchange the same as an ecommerce marketplace?

No. An ad exchange sells ad placements on the websites and apps of many publishers. Ads on Shopee or TikTok Shop, the large ecommerce marketplaces in Vietnam, fall under retail media. They run inside each marketplace’s own ad system and never pass through an ad exchange.

If you are considering programmatic display and are not sure whether to buy through a DSP or directly from publishers, you can talk it over with Adtek through our contact page.