People are always finding new uses to Google. One of the latest, and certainly one of the most interesting is the ability to earn money through google.
The Google Cash 3rd Edition book illustrates on this topic. Basically, the book details a home based business that takes as its starting point a program known as Google AdWords, which lets you display advertisements on Google and its advertising network. The ad themselves are created by you; you have to choose some selected keywords, which relate to your business. When people make a Google search that employs any of the keywords you provided, your ad will be displayed. This means that your ad will be shown to somebody who is already interested in that topic. As far as running costs are concerned, you detail the amount of your budget, and you are charged only in the event someone clicks on your ad; there is no charge itself for displaying an ad. 
