Behavioral targeting

Behavioral targeting infers what you might want from what you have done. If you have been reading car reviews, visiting dealer sites and searching for loan rates, you are likely to be placed in an "auto intender" audience segment and shown car ads, even while reading about football.

Traditionally it relied on third-party cookies, mobile ad IDs, cookie syncing and third-party data to follow users across sites and apps. Walled gardens do it within their own ecosystems using logged-in data. Retargeting is a specific form: targeting people who interacted with your own site or app.

It is effective but privacy-intensive, and it is the main target of privacy regulation. GDPR and the ePrivacy rules generally require consent in the EU; California's CCPA / CPRA gives users the right to opt out of "cross-context behavioral advertising"; the Digital Services Act bans profiling-based ads to minors on platforms; and Apple's App Tracking Transparency requires permission for cross-app tracking. Its alternative is contextual targeting.

Think of it like this

Behavioral targeting is like a shop assistant who recognises you from other shops you visited and says, "I heard you were looking at tents."

An example

A travel site in the US shows hotel ads for Tokyo to users who searched Tokyo flights on other sites in the past week, using a data provider's cookie-based segment.