Third party ad serving refers to the practice of using a third party ad server to deliver an ad instead of using the publisher (or network) ad server for uploading ad and configuring click-through URLs. The third party ad server may be an agency server which centralises campaign reports or a third party server from an ad technology vendor.
Third party ad serving through agency ad server enables advertisers to get consolidated reporting and creative optimization across all publishers and ad networks used for a single campaign.
When using third party ad serving, the creative is hosted on the third party server and the publisher ad server hosts only a third party tag which redirects to the third party ad server to deliver the creative.
An example of IFRAME third party ad tag:
Third party ad serving may raise issue for publishers which can’t control the ultimate delivery of the ad:
Due to these issues, publishers and ad networks severely restrict the possibilities of third party ad serving. They use certified third party lists or third-party ad serving programs and restrictive guidelines.
Third party ad serving illustrated by Yahoo UK: