What is a third-party cookie?
A third-party cookie is a cookie set by a domain other than the website a person is visiting, often an ad network or analytics provider. It can follow a person across different sites, which is why browsers and privacy laws restrict it.
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How they work
When a page includes content or code from another company, that company can set its own cookie in the visitor's browser. It can read the cookie again on any other site that includes the same provider.
That cross-site reach is what made them useful for ad targeting, frequency control, and conversion measurement.
Why they're fading
Safari and Firefox restrict third-party cookies by default. As of late 2026, Chrome has kept its existing approach to user choice rather than a broad deprecation. Browser policies can change, so review current documentation.
Privacy laws and consent rules also limit how they can be used.
What to use instead
Advertisers lean more on first-party data, server-side tracking, consent-based measurement, and modeled reporting. Building these now makes your tracking less dependent on any single browser's decisions.
Common questions
What's the difference between first-party and third-party cookies?
A first-party cookie is set by the site the visitor is on. A third-party cookie is set by a different domain embedded on that site.
Are third-party cookies going away?
Some browsers already restrict them. As of late 2026, Chrome has kept existing user choice rather than broadly removing them. Plan for browser-specific restrictions and consent requirements instead of assuming one universal phase-out date.
How do third-party cookies affect retargeting?
Retargeting often depends on them to recognize a visitor across sites. When they're blocked, audiences shrink, so first-party lists and other methods matter more.
Can I still measure conversions without them?
Yes, though less completely. First-party tags, server-side tracking, and platform modeling help close the gap.
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