Google is letting users of Google Search and Gmail block ads.

The company announced that it is placing a “Why these ads?” link on Google search results and Gmail, and when the link is clicked, you get an explanation about why you’re seeing specific ads. Users can also access the ads preferences manager for search and Gmail.

“Here, the user can choose to block ads from specific advertisers or opt out of personalized ads,” explains Group Product Manager Ginsu Yoon. “Because we can show fewer, more relevant ads when users have opted-in to see personalized ads, we describe these benefits with text and video to help them make an informed choice.”

Here’s that video:

“As an advertiser, you might wonder how these changes could impact your AdWords performance,” says Yoon. “When a user opts out of personalized ads on search and Gmail, your ads can still reach them but the targeting might be a bit less precise. If users block your ads, they won’t see your ads in the future. The number of blocks you’ve accumulated does not directly affect calculations of your Quality Score and Ad Rank.”

That’s not the only targeting change Google has unleashed on advertisers this week. They also announced changes to location targeting, and the termination of polygon targeting altogether.

Google’s announcement in relation to Gmail comes at a particularly interesting time, as Google is getting ready to (finally) launch a Gmail app for the iPhone. Why is this interesting? Because iCloud comes with ad-free email. If you followed its announcement earlier this year, you may recall Steve Jobs making a big deal about this.

“”No ads,” he said. “We build products that we want for ourselves, too, and we just don’t want ads.”

Perhaps realizing that a lot of iPhone users might feel the same way, Google makes this announcement. Or maybe it’s just coincidence.