There are many marketing opportunities available to internet-based businesses. One of those is 'pay-per-click' advertising, whereby you only pay when somebody clicks on a link to your site, rather than when they view an advertisement. Ideally, you want to be generating a return on each 'per-click' investment that exceeds the performance you could achieve by using those expense dollars in other areas of the company or investing them. To measure ROI, you need to carefully track your conversion rates and costs so that you know which sales can be tracked back to a particular campaign.