Site-based retargeting uses cookies to stay in front of previous site visitors. When someone visits your website, a few lines of code provided by your retargeter will drop an anonymous browser cookie. This cookie is a small file that stores information. The cookie will store the site visit, but does not store any sensitive information, such as the site visitor's name, address or any other piece of information that might personally identify the visitor.

When someone comes to your site, a cookie is dropped, and eventually, they leave and visit another site. The cookie lets your retargeting provider know when one of your bounced visitors appears on another site. If there is available ad space, your retargeting provider will bid on that space in real-time, aptly named real-time bidding or RTB, and if they are the highest bidder, will secure the ad space before the page loads.

This entire process is automated and occurs within a fraction of a second. By the time the page loads, the ad space will have been purchased and your ad will appear alongside the page content.