Ad Network

An ad network is a company that aggregates advertising inventory from many publishers and sells it to advertisers, acting as a broker between supply and demand. Rather than negotiating with each website individually, an Advertiser buys through the network, which matches their budget to available slots across its pool of sites.

How it works: Publishers hand unsold or remnant inventory to the network, often via an ad tag on their pages. The network bundles that inventory, frequently by category, audience, or geography, and serves ads into it on the advertiser's behalf. It handles targeting, delivery, billing, and reporting, taking a margin on the spend. Historically ad networks predate programmatic exchanges, but most now plug into Ad Exchange marketplaces and real-time bidding to source and price inventory.

Why it matters: Ad networks give advertisers reach and a single point of buying, while giving publishers a way to monetize inventory they could not sell directly. The trade-off is less transparency: it can be hard to see exactly which sites ran an ad and at what price. Specialized networks focus on a format or vertical, such as a Native Ad Network that deals only in content-recommendation placements. Distinguishing a network from an exchange matters: networks curate and resell bundles, while exchanges run open auctions.

Related terms: the Native Ad Network, Ad Exchange, Publisher, and Advertiser.