Behavioral retargeting (also known as behavioral remarketing, or simply, retargeting) is a form of online targeted advertising by which online advertising is targeted to consumers based on their previous Internet actions, in situations where these actions did not result in a sale or conversion.
Some noted companies in the behavioral retargeting space include: Criteo, AdRoll, Retargeter (acquired by SellPoints), Chango (acquired by Rubicon Project), MyThings, Steelhouse, Perfect Audience (acquired by Marin Software), and Google. 
In its most basic form, retargeting serves ads to people more frequently after they have left a publisher's website. The users will be shown retargeting ads as frequently as possible unless a frequency cap has been placed by the advertiser. In practice, most publishers sign up for displaying ads from ad networks instead of directly negotiating with the advertiser to display their ads. Some advertisers specialize in retargeting, while other companies have added retargeting to their list of methods of purchasing advertising. Retargeting helps companies advertise to website visitors who leave without a conversion - this accounts for about 98% of all web traffic.
Retargeting marks or tags online users who visit a certain brand website with a pixel or a cookie, and then serves banner ads only to the people who have shown at least some amount of engagement with the original brand. Retargeting ad campaigns usually run on lower cost media, such as display ads, which not only increases effectiveness by specifically targeting an interested audience, but also improves the overall ROI of the advertiser.
Personalized retargeting, a related practice, differs from behavioral retargeting in that it allows an advertiser to display a banner created on-the-fly for a particular consumer based on their specific browsing behaviour. For example, if a consumer visits an advertiser's website and browses products A, B and C - they will then be retargeted with a display banner featuring the exact products A, B and C that they previously viewed. This is typically restricted to the visitor's browsing on a single website.
A refined version of personalized retargeting improves on re-engagement of customers. If a customer begins an online order, for example, but fails to complete, a flag indicates they had interest in the product being ordered. Later, ads showing the product of interest can be custom-linked to point back into the order system. When the user clicks on the ad, they are returned to incomplete order. Such an implementation requires that the order system support deep linking or other retargeting services.
- Behavioral targeting
- Deeplink (company)
- Email retargeting
- Personalized retargeting
- Search retargeting
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- "Top Online Display Retargetings". Thalamus. Thalamus. Retrieved 12 September 2015.
- "The Future of Retargeting, Remarketing and Remessaging". Marketing Land. Retrieved 30 July 2012.