Cost per acquisition (CPA), also known as cost per action, pay per acquisition (PPA) and cost per conversion (CPC), is an online advertising pricing model where the advertiser pays for a specified acquisition – for example a sale, click, or form submit (e.g., contact request, newsletter sign up, registration etc.) Cost per acquisition (CPA), also known as cost per action, pay per acquisition (PPA) and cost per conversion (CPC), is an online advertising pricing model where the advertiser pays for a specified acquisition – for example a sale, click, or form submit (e.g., contact request, newsletter sign up, registration etc.) Direct response advertisers often consider CPA the optimal way to buy online advertising, as an advertiser only pays for the ad when the desired acquisition has occurred. The desired acquisition to be performed is determined by the advertiser. In affiliate marketing, this means that advertisers only pay the affiliates for leads that result in a desired action such as a sale. This removes the risk for the advertiser because they know in advance that they will not have to pay for bad referrals, and it encourages the affiliate to send good referrals.