Ad server

An ad server is the system that decides which advertisement to show in a given slot, delivers the creative, and records the impression, click and other events that advertisers and publishers are billed and paid on.

Publisher ad servers (Google Ad Manager is the largest; SpringServe, FreeWheel and Publica are named alternatives in the US remedies proceedings) hold the publisher's direct-sold campaigns, run the final decision between direct deals and programmatic bids from header bidding or an exchange, and produce the logs of record. Advertiser ad servers hold the creative and count impressions independently of the publisher. In retail media the ad server is the component that ranks sponsored products against organic results and serves display; vendors such as Kevel sell it as "Ad Server APIs" (Kevel, accessed 17 October 2026).

The ad server matters for measurement because its logs define the impression. The IAB/MRC guidelines count an impression only when the ad "has begun to render" and require viewability to be measured to MRC thresholds where applicable (IAB/MRC, January 2024). It matters for the supply chain because SupplyChain v1.1 (public comment to 21 August 2026) adds ad servers, wrappers and SSAI platforms as custody-taking nodes in the schain (IAB Tech Lab, 23 June 2026).

Example: a publisher's ad server receives a header-bidding price of $3.00 and a direct campaign booked at $2.50 CPM with a delivery goal; its rules decide whether the goal outranks the price, serves the chosen creative, and writes the impression to the log that the publisher reconciles against the SSP's report.

Related: header bidding, log-level data, SupplyChain object, SSAI.

Source: IAB/MRC, "Retail Media Measurement Guidelines" (January 2024), impression definition; IAB Tech Lab, SupplyChain v1.1 (June 2026).

1. Kevel, accessed 17 October 2026
2. IAB/MRC, January 2024
3. IAB Tech Lab, 23 June 2026