The common business model of search engine providers such as Google or Bing (MSN) is the insertion of thematically relevant text ads.
<note important>The world's most widely used web search engine is Google. Their search engine marketing is called Adwords™, which expanded continuously since 2000 - thus, now at three levels of context-sensitive ad placements.</note>
The three levels are:
http://de.wikipedia.org/wiki/Google_AdWords (source) <note tip> And so the network operates in the rough: (1) Advertisers manage their campaigns using the Adwords system of key terms, to interest users for their own web content. (2) Depending on the entered words in the text box relevant ads are displayed. (3) The order is measured by the relevance and according to an auction model based on the willingness of advertisers. (4) Click the visitor arrives on an ad, he deposited on the landing page of the advertisers. Costs are again only when the user clicks on the ad. The insertion without a click is now free.</note>