Cost Per Acquisition (CPA), otherwise known as Cost Per Action, is a form of affiliate marketing where advertisers pay for a specific form of acquisition or action to be taken. Acquisitions can range from clicks to requests for service, to filling out forms, to installs and downloads depending on the details of the contract. CPA affiliate marketing has become a multi-billion dollar industry and many affiliate marketers partake in CPA affiliate marketing without even realizing it. CPA is simply a certain form of affiliate marketing.