A concept that has created an entire industry and a concept that has changed business and marketing on the Web. We are of course talking about the simple concept of Pay per Click. The concept is simple. Advertiser pays the publisher for a click/visit originating from the publisher's Web site. Pay per Click is now an industry of it own. Search engines sell pay per click advertisements, publishers sell ay per click advertisements often with the help of publisher networks and the science of managing pay per click campaigns requires specialists and specialized software. One can say with strong confidence that the Pay per Click business model is the most used business model in Web publishing today.