Google is testing responsive AdSense ad units to cater for the increasing number of mobile websites that adapt to different screen sizes.
The responsive ad units fit a wide range of Google’s standard sizes, one of which must be specified when creating the ad. The units have been designed to work with the company’s asynchronous tag code, which ensures that web pages still load even if the ad is having trouble rendering. 
The company says it is still working on a way to get ads to dynamically adjust after they have been served, if the viewer changes the orientation of the screen, for example, acknowledging that this has been requested by AdSense users.
