Reference / Glossary / Infrastructure and standards
Third-Party Cookie
A cookie set by a domain other than the one the user is visiting, which lets an ad tech company recognize the same browser across sites. Third-party cookies underpinned retargeting, frequency capping, third-party data, and view-through attribution on the open web. Safari and Firefox block them by default; Chrome, after years of delays under its Privacy Sandbox program, abandoned plans to remove them in 2025 and instead kept them with user controls.
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Cite this entry:
Agency Echelon. "Third-Party Cookie." Agency Echelon Reference, reviewed September 2026. https://agencyechelon.com/reference/glossary/third-party-cookie/