Google has announced that AdSense publishers will soon be able to choose whether to accept advertisements from other ad network companies, as well as AdSense itself, in a change to how ads are served.

Any network that is Google-certified — that is, the ad company adheres to user privacy, ad quality and speed standards — can bid for ad positions previously exclusively available to AdWords advertisers.

Publishers are guaranteed that the highest revenue ads will make it onto their sites, and have complete control over which networks, if any, are allowed.

Third-party ad networks won’t be permitted to collect data from publisher sites to build their own interest-based advertising models, but can show ads based on data already collected elsewhere.

These changes will be rolled out over the next few months. It will be interesting to see what impact these have on publisher earnings, and whether AdWords advertisers notice any difference.