What Is a First-Party vs. a Third-Party Cookie?

A first-party cookie is set by the domain a visitor is directly interacting with; a third-party cookie is set by a different domain than the one in the browser's address bar, typically by an embedded ad or tracking script. Browsers increasingly restrict or block third-party cookies by default, part of why server-side tagging and cookieless tracking methods have grown more common.

The distinction matters because the two are treated very differently by browsers and regulators. First-party cookies, used for things like keeping shopping cart contents intact, are generally allowed with minimal friction. Third-party cookies, historically the backbone of cross-site ad tracking, are the ones browsers like Safari (Intelligent Tracking Prevention (ITP)) actively block, and the ones consent laws scrutinize most heavily. A site’s actual dependency on third-party cookies is worth knowing precisely, since it’s disappearing as a viable method regardless of consent status.