What is marketing? Cost per Action, and sometimes misconstrued by other marketing models as cost per purchase, is a dynamic online advertising measure and pricing model referring to an action, such as a sign-up or a download, by a customer or visitor to a website. The advertiser, who might be a network of websites or an individual online business, pays the website owner a fixed amount per action group, such as signing up for a newsletter, which gives them access to a list of email addresses. The subscriber, who might be someone new to the Internet, only uses the cpa services once, then deletes his or her email address. The advertiser can track the number of sign-ups and other activity on their website using an easy-to-use website interface.