Cost Per Action or CPA (sometimes known as Pay Per Action or PPA) is an online advertising pricing model, where the advertiser pays for each specified action (a purchase, a form submission, and so on) linked to the creative.

Direct response advertisers consider CPA the optimal way to buy online advertising, as a merchant only pays for the ad when the desired action has occurred. An action can be a product being purchased, a form being filled, etc. (The desired action to be performed is determined by the merchant.) The CPA can be determined by different factors, depending where the online advertising inventory is being purchased.

There are other advertising pricing structures:

• CPC - Cost per click Through
• CPM - Cost per Impression
• CPL - Cost per lead (lead usually meaning a free registration)

See also: Campaign Method