Yahoo and Google are now working together on ads. Yahoo announced in a post on its corporate blog that it has teamed up with the search giant on contextual advertising.

The two companies have signed a global, non-exclusive agreement for Yahoo to display contextual display ads from Google on various Yahoo properties and “certain co-branded sites” using Google’s AdSense for Content and AdMob advertising offerings.

“By adding Google to our list of world-class contextual ads partners, we’ll be able to expand our network, which means we can serve users with ads that are even more meaningful,” says Yahoo in the post. “For our users, there won’t be a noticeable difference in how or where ads appear. More options simply mean greater flexibility. We look forward to working with all of our contextual ads partners to ensure we’re delivering the right ad to the right user at the right time.”

It wasn’t that long ago that Google Executive Chairman Eric Schmidt expressed interest in partnering with Yahoo, years after the companies tried to partner on a search advertising deal, which was shut down by the threat of regulation. Yahoo ended up partnering with BIng in that space, and so far, this new announcement will do nothing to change that.

Again, this is a non-exclusive agreement, and Yahoo is still partners with Microsoft (in addition to others) in this area too.

“Every day, people turn to Yahoo! for their daily habits — like search, weather, news or more. At Yahoo!, we’re focused on doing everything we can to make the user experience inspiring and engaging. One way we do that is by providing relevant and well-targeted content — whether that be editorial or advertising content,” says Yahoo. “Say you’ve been shopping for boots. If you see an ad for boots, that’s instantly going to pique your attention more than an ad for, say, a car battery. That’s better for users. This is why contextual advertising is such a powerful tool.”

According to the company, users won’t see much of a noticeable difference in how and where ads appear.

While this isn’t the huge news that an exclusive Google/Yahoo search advertising deal would be, it’s very interesting to see the companies working together, especially considering the rivalry between Microsoft and Google. It’s also interesting given the fact that Yahoo is now run by longtime Googler Marissa Mayer, who has brought other Googlers along for the ride at Yahoo. Will this relationship blossom into something more between Yahoo and Google? Time will tell.