Retargeting works by displaying ads to individuals who are contained within your retargeting audiences. Retargeting audiences are collected in many different ways but are primarily gathered by identifying previous visitors to your website. This identification process is possible by adding “cookies” to the visitor’s browser via a pixel or code snippet that has been placed within the website code. Because retargeting cookies and pixels are specific to each ad platform, these audiences are specific to each ad platform and grow independently from each other.
Most retargeting ad impressions are delivered by use of the Google Display Network and a few social media ads platforms (primarily Facebook). Although in most cases, the ad impressions they deploy on are still through Google Ad Words or Facebook, there are many “ad networks” that provide remarketing platforms.
Marketers can create retargeting audiences based on the amount of time since a site visitor’s last visit to a specific web page or site. These durations can vary by days, weeks, months and, in the case of Google Ad Words remarketing, years. In these time periods, advertisers can deploy ads to incentivize remarketing audiences to revisit the site to buy products/services or provide them with new offerings.