There are currently four different compensation models for "affiliates" (or Publisher who promotes the Advertisers offers via its own website, newsletter, eZine or other marketing channels) that generate traffic to a merchant (Advertiser) website: pay-per-impression, pay-per-click, pay-per-lead and pay-per-sale or combination of models.

Like the Impression model, the Pay model was popular during the dot com boom at the end of the - due to rampant problems with click fraud - was mostly abandoned by merchants for advertisements on other websites.

The PPC model was kept alive by the PPC search engine Goto. which became Overture. and is now owned by Yahoo! and renamed from "Yahoo! Sponsored Search" to "Yahoo! Search Marketing."

The big comeback of PPC came when Google launched Ad Sense in 2003, the birth of contextual advertising. "Contextual Advertising" means that a search engine scans pages to match ads with the context of a page. For more help visit to:www.affiliate-directories-online.com. Google Ad Words Advertisers have the choice whether or not they want their ads being displayed on Ad Sense publisher websites, what Google calls their "Content Network".

To best explain Google Ad Sense, here is a quote from Google's History at Google's corporate Website. Google Ad Sense:

"... Offering web sites of all sizes a way to easily generate revenue through placement of highly targeted ads adjacent to their content. For more help visit to: www.firesale-automator.com. Google Ad Sense technology analyzes the text on any given page and delivers ads that are appropriate and relevant, increasing the usefulness of the page and the likelihood that those viewing it will actually click on the advertising presented there."

Classic PPC search engine marketing is not affiliating marketing. It is an entirely different type of Internet marketing and has only some technical details in common with old PPC/CPC affiliate marketing. Ads are primarily displayed at the search engine search results pages (SERPs) next to organic, free search results.

Contextual advertising introduced with Google Ad Sense is also not affiliate marketing since there is no direct partnership between the advertiser, who creates and pays for the ad, and the publisher who displays the ads on his website.

PPC and Contextual advertising are generally referred to as search engine marketing (SEM) and is often wrongly confused with search engine optimization (SEO). SEO is about improving the ranking of a site in the organic, free SERPs at major search engines via technical means and deep understanding of the complicated ranking algorithms used by modern search engines.

This is a new compensation model. No official abbreviation exists yet. The advertiser (merchant) pays the publisher site a flat $x.xx amount in commission for phone calls received from potential customers in response to a specific ad. Recently developed call-tracking technology provides a bridge between online and offline advertising. Pay-Per-Call advertising is still in its infancy.

Pay-Per-Call advertising is neither search engine marketing (SEM) nor affiliate marketing. It is expected to become, within the next few years, the fourth major type of Internet marketing, next to affiliate marketing, search engine marketing and search engine optimization.