Third-party cookies
The connective tissue of old adtech — cross-site memory that browsers have spent years pulling apart.
- Set by
- a domain other than the site
- Enabled
- cross-site tracking, retargeting
- Blocked by
- Safari, Firefox, then Chrome moves
- Successor
- first-party data, Privacy Sandbox
Forms & parts of speech
What they did
A first-party cookie is set by the site you are on; a third-party cookie is set by another domain embedded in the page, like an ad network. That cross-domain cookie let companies follow users from site to site.
This cross-site memory powered classic adtech — behavioural targeting, retargeting the shoe you looked at, frequency capping, and multi-touch attribution. It was the connective tissue of the open-web ad ecosystem.
Why they are going away
Privacy concern and regulation turned browsers against them. Safari and Firefox blocked third-party cookies years ago; Chrome's approach has shifted repeatedly but the long-term direction is clear — cross-site cookie tracking is ending.
The successors are first-party data, contextual targeting, server-side measurement like the Conversions API, and privacy-preserving proposals such as the Privacy Sandbox. Marketers who built on third-party cookies have had to rebuild on consented, first-party foundations.
The brand rebuilds on first-party data — logged-in users, email, and consented signals — plus contextual placements and server-side measurement. The new foundation is smaller but durable, where the cookie-based one was eroding under the brand's feet.
Benchmarks
Browser timelines have shifted repeatedly, so treat any deprecation date as provisional. The durable planning assumption is that cross-site cookies are unreliable.
Ranges are illustrative; every published figure is cited from a named public source or labelled “RGM analysis.”
Synonyms & antonyms
Synonyms
Antonyms
Usage trends
Search interest for this term over the last five years:
Common questions
- What are third-party cookies?
- Cookies set by a domain other than the site you are visiting, used to track users across sites for targeting, retargeting, and attribution.
- Why are third-party cookies being deprecated?
- Privacy concerns and regulation. Safari and Firefox already block them and Chrome has moved to restrict them, ending durable cross-site cookie tracking.
- What replaces third-party cookies?
- First-party data, contextual targeting, server-side measurement like the Conversions API, and privacy-preserving approaches such as the Privacy Sandbox.
Related tools & calculators
Resources & people to follow
- referenceGoogle — Privacy Sandbox overview
- referenceRGM analysis — post-cookie measurement
Curated, non-competitor resources verified per term.