Those of you who carefully check your AdSense ads may have noticed that they're now being served primarily from a DoubleClick URL rather than the URL you're used to. We heard some confusion over this topic from a few publishers, and we'd like to clarify a few misconceptions.

This change in the URL where the ads are served from is due to the DoubleClick ad serving cookie that we launched on the Google content network last year. Since this cookie is on the domain, we've had to update our URLs to point to, as well as to give you the associated benefits such as frequency capping and improved attribution.

However, this is only an infrastructure change -- there haven't been any changes to the ads themselves. The ads you see are still coming from AdWords advertisers or third-party advertisers, just as they were before, and it's not the case that you're now receiving 'DoubleClick ads' instead of 'Google ads'.

Along the same lines, we'd like to reassure you that this new URL hasn't changed the targeting of ads on sites. As a quick refresher, each ad that appears on your pages can be contextually targeted, placement-targeted, or soon, interest-based. With contextual targeting, ads are matched to your content based on keywords selected by advertisers, while with placement targeting, advertisers select specific ad placements where they'd like their ads to appear. And with our latest addition of interest-based advertising, advertisers will be able to reach users based on their interests or previous interactions with an advertiser's site.

By allowing all types of ads to compete for the ad space on your site, you'll increase the competition for your ad space to help ensure that you're maximizing your earnings potential. However, you can also continue to prevent specific ads from appearing by using your Competitive Ad Filter and the Ad Review Center.

We hope this helps alleviate any concerns you may have had about the URL switch.