Yahoo has signed a global, non-exclusive agreement with Google to display ads on various Yahoo! properties and certain co-branded sites using Google’s AdSense for Content and Google’s AdMob services.
This means text/image ads set up on Google Adwords now can be displayed on various Yahoo! properties too!
Yahoo gets additional revenue for unused ad slots. This can possibly lead to higher ad revenue compared with its current ads because of Google’s powerful contextual targeting capabilities which bring more relevant ads that people might click on.
For Google, its Display network gets even larger given the size of Yahoo!’s online properties.