An advertisement for hiking boots on a hiking article does not need to know who you are.
It needs to know what the page is about.
That is the simplest form of contextual advertising.
Behavioral targeting works from a different question.
Instead of asking What is this page about?, it asks something closer to What does this person appear to be interested in?
Context can be enough
Google Ads describes contextual targeting as matching ads to content using topics, placements, keywords, language, and other signals about the page or placement. See Google Ads’ contextual targeting documentation.
In the clean conceptual version, a gardening page can show gardening ads because the page is about gardening.
The advertiser does not need a six-month browsing history to make that decision.
Behavioral advertising instead uses information associated with a person or device: prior browsing, app activity, searches, purchases, inferred interests, demographic assumptions, or membership in audience segments.
That requires some mechanism for remembering or recognizing the audience.
The labels can blur in real systems
This is where terminology becomes slippery.
A product may call part of its system contextual while also using other signals such as location, recent activity, account information, or campaign optimization.
Google’s own contextual-targeting documentation notes that several factors can contribute to ad selection, including content and, in some configurations, a visitor’s recent browsing history.
So contextual should not be treated as a magic privacy label.
The useful research question is narrower:
What information was actually used to choose this ad?
If the decision came only from the content and immediate context, the system needs far less personal history.
If it depended on a durable profile, it has crossed into behavioral targeting even if the page topic also mattered.
Less profiling does not guarantee better or worse advertising
Contextual advertising has obvious limits.
A page about cameras may be read by somebody who already bought one yesterday. A behavioral system may know that and choose something else.
On the other hand, behavioral profiles can be stale, wrong, or based on somebody else using the same device.
Performance therefore depends on the publisher, advertiser, product, measurement method, and implementation.
It is not responsible to declare one method universally superior.
The privacy difference is easier to state.
Contextual targeting can often operate with much less long-term personal data because the page supplies the targeting signal.
Behavioral targeting needs the person or device to supply it.
That is a significant architectural choice.
The Surveillance Economy often treats persistent identity as the natural price of advertising.
Contextual advertising is evidence that advertising can exist without making every reader carry a dossier into the auction.