Search engine advertising is the generic name for the sponsored links that appear alongside organic search engine results. All major search engines offer a self-serve advertising system where advertisers can place competing bids for the right to take the most prominent position within the paid listings. The advertiser can decide what amount they literally want to "pay-per-click" (abbreviated PPC).
Things you should know
Here are the most popular pay per click advertising services offered by search engines. Although they go by different names, they all function using the same basic bidding principle.
The vast majority of Google's 23 billion dollars in revenue in 2009 came from Google AdWords.
Yahoo sponsored search
Yahoo! is technically the inventor of the Pay-Per-Click model through their acquisition of the now defunct Overture dot com, the original PPC search engine. But Google was first to implement PPC in it's current incarnation.
Create an account on AdCenter to start search adverstising on Bing.
Ask Sponsored Listings
Ask.com is the 4th largest search engine.
Organic search results listings get more clicks, and provide better value over time. But sponsored listings have the advantage of near instant turnaround.