Header bidding is a programmatic-advertising technique in which a publisher offers its ad inventory to multiple demand sources (SSPs and exchanges) simultaneously, before its primary ad server is called, so those sources compete in a unified auction.
Definition
Header bidding is a programmatic-advertising technique in which a publisher offers its ad inventory to multiple demand sources (SSPs and exchanges) simultaneously, before its primary ad server is called, so those sources compete in a unified auction. It replaced the older "waterfall", where demand sources were called one after another in a fixed priority order that systematically underpriced inventory by not letting lower-priority buyers outbid higher-priority ones.
The result for publishers is higher yield, because every impression is exposed to real simultaneous competition, and more transparency into what each source will actually pay. The costs are added page-latency risk (the auction runs while the page loads) and technical complexity, both of which are managed by running the auction server-side or with strict timeouts.
In context
Header bidding is relevant to the iGaming ecosystem mainly on the supply side: the ad networks and publishers that sell push, popunder, native and display inventory to iGaming media buyers often monetise through header-bidding setups, and it is part of why inventory quality and pricing vary so much across sources. For an affiliate that also publishes a content site with its own ad slots, header bidding is the mechanism to get a fair price for that inventory rather than leaving money on the table with a waterfall.
For the media buyer purchasing iGaming traffic, the take-away is indirect but useful: the price paid at the buy side is the outcome of these auctions, arbitrage and fees sit between the advertiser's bid and the publisher's payout, and "cheap" inventory is often cheap because it lost the real auctions elsewhere. It reinforces the standard discipline — judge a source on downstream FTD value, not on CPM or CPC, because the supply chain's pricing does not tell you anything reliable about traffic quality.
Worked example
An affiliate's content site earns a low flat CPM from a single ad network on a waterfall. Adding header bidding with four demand partners and a 300ms timeout raises average display RPM by 35% with no measurable effect on Core Web Vitals, because the auction runs server-side.
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