What is a third-party cookie?
Why does it matter to a marketer?
Some ad tracking and audience building can depend on cookies that travel across sites. If that sort of cookie is blocked or limited, the numbers can change. Reports can show fewer conversions, or credit them differently.
So the useful question is not "are third-party cookies dying". It is which parts of your own measurement rely on them, and what is left if they go. Safari's rules are one example of a browser limiting cross-site tracking: see Intelligent Tracking Prevention (ITP). Google's own initiative to build alternatives in Chrome is covered in Privacy Sandbox.
Our view: do not take a platform's word that tracking is unaffected. Check which of your conversion counts come from browser cookies, and which from data you collect yourself. Our guide to an ecommerce tracking audit sets out the checks that change a budget decision.
Worked example
Easily confused with
Third-party cookie vs First-party cookie
Stored by the site you are visiting. It is not a stand-in for first-party data.
Third-party cookie vs First-party data
Data a brand collects directly from its own interactions with customers, such as orders, accounts and email sign-ups. Data, not a cookie.
Third-party cookie vs Cookies in general
"Cookie" is the piece of data in the browser. First-party and third-party describe who set it.
FAQ
Is a third-party cookie the same as a cross-site cookie?
Google's documentation says third-party cookies are really cross-site cookies1. The two names describe the same thing from different angles.
Are third-party cookies illegal?
That is a legal question, not a marketing one: your counsel decides.
Sources
- What are third-party cookies?Primary source
Let’s find what’s actually working.
Next step. See how much of your reported revenue holds up on explicit assumptions with the Is your ROAS real? calculator.