Cost Per Action or CPA (as it is often initialized to) is a phrase often used in online advertising and online marketing circles.

CPA is considered the optimal form of buying online advertising from the advertiser s point of view. An advertiser only pays for the ad when an action has occurred. An action can be a product being purchased, a form being filled, etc. (The desired action to be preformed is determined by the advertiser.)

A related term, effective Cost Per Action or effective Cost Per Action, is used to measure the effectiveness of advertising inventory purchased (by the advertiser) via a Cost Per Click, Cost Per Impression, or Cost Per Time basis.

The CPA can be determined by different factors, depending where the online advertising inventory is being purchased.

Other common forms, of charging for advertising, include:

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