A system used in online marketing in which the advertiser pays only when a sale or other type of conversion has been made. It can also be described as the cost of selling a particular product or service via a website. A CPA marketing model is one in which the publisher takes the bulk of the advertising risk. This type of pricing program is most advantageous to the advertiser.

The actions defined in a cost-per-action agreement relate directly to some type of conversion, with sales and registrations among the most common. This does not include deals based solely on solely clicks, which are referred to specifically as cost-per-click or CPC.

The cost-per-action (CPA) model is at the other end of the spectrum from the cost-per-impressions model (CPM), with the cost-per-click (CPC) model somewhere in the middle. In a CPA model, the publisher is taking most of the advertising risk, as their commissions are dependant on good conversion rates from the advertiser's creative units and Web site.

Marketers looking for cost-per-action deals have several options. Publishers with considerable excess inventory may be willing to consider nonstandard offers. Sites specializing in incentive programs are in a position to offer CPA pricing on various types of leads, although the usual caveats concerning incentivized traffic still apply. Perhaps the most widespread use of performance-based pricing is affiliate marketing, whereby merchants/advertisers determine what actions they want to reward and how much they are willing to pay