Third Party Cookies

Third party cookies are set by a domain different from the one the user is currently visiting. The classic example is an advertising script embedded on many websites that reads the same cookie across all of them. This makes it possible to follow a user's browsing behaviour across domain boundaries.

Browser policy and phase out

Safari has blocked third party cookies by default since 2020, Firefox since 2019. Chrome has repeatedly postponed its phase out but is moving in the same direction. Advertisers who built measurement and retargeting on third party cookies lose signal quality and must shift to first party data, server side tracking and contextual targeting.

Privacy and consent

In the European Union, third party cookies require explicit user consent because they are typically not technically necessary. Cookie banners must document the consent before any third party script is loaded. If the script loads before consent, the setup is not GDPR compliant.

In everyday marketing

Anyone building tracking today should primarily rely on first party data, identifiers created on the owner's own domain. Conversion APIs of the major ad networks replace part of the pixel signals without requiring a third party cookie in the browser. For many use cases, a clean mix of UTM parameters, logged in user context and server side event handoff is enough.