Pay per click (PPC) is an Internet advertising model used on websites, where advertisers pay their host only when their ad is clicked. With search engines, advertisers typically bid on keyword phrases relevant to their target market. Content sites commonly charge a fixed price per click rather than use a bidding system.

Cost per click (CPC) is the sum paid by an advertiser to search engines and other Internet publishers for a single click on their advertisement which directs one visitor to the advertiser's website.

In contrast to the generalized portal, which seeks to drive a high volume of traffic to one site, PPC implements the so-called affiliate model, that provides purchase opportunities wherever people may be surfing. It does this by offering financial incentives (in the form of a percentage of revenue) to affiliated partner sites. The affiliates provide purchase-point click-through to the merchant. It is a pay-for-performance model: If an affiliate does not generate sales, it represents no cost to the merchant. Variations include banner exchange, pay-per-click, and revenue sharing programs.