Pay per click advertising on search engines such as Google and Bing. On Google the adverts are displayed either at the very top of the search results with an orange background, on the right hand side or in both these places. Advertisers pay Google each time someone clicks on their advert. It is often referred to by the letters PPC. Many pay per click providers exist, Google AdWords, Yahoo! Search Marketing, and Microsoft adCenter are the three largest operators. 