Some mobile app sellers include an advertising element in their revenue models. These apps include mobile ads that display messages from advertisers(other than the seller of the app). One common way to include ads is to display them in a small bar at the bottom of the app screen. Some apps include advertising that appears on a part of the screen or as a separate screen that must be clicked through to get to the app. The advertising space on mobile apps is sold in the same way that banner advertising on Web sites is sold(which you learned about in Chapter 5)