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A first-party cookie is set by the website you are actually visiting. A third-party cookie is set by a different domain than the one in your address bar.
That single distinction — who set the file — is the whole difference. Everything else follows from it: what each is used for, which one browsers block, and which one the phrase “a cookieless future” is actually about.
What a cookie is
A cookie is a small text file a website asks your browser to store, and which the browser sends back on later visits. It exists because the web is otherwise stateless: without it, a site has no way to know that the person loading this page is the same person who loaded the last one.
Cookies were created to solve mundane problems — keeping you logged in, remembering what is in your basket. The advertising uses came later.
First-party cookies
Set by: the site you are on.
Typically used for: keeping you signed in between pages, remembering items in a shopping basket, storing language or currency preferences, and site analytics.
Status: working normally in every major browser. No browser blocks them by default, and no plan exists to.
If first-party cookies stopped working, the web would largely break — you would be logged out on every page load. This is why they were never part of the deprecation conversation.
Third-party cookies
Set by: a domain other than the one you are visiting — usually an ad tech company whose code is embedded in the page.
Typically used for: recognising the same person across different websites. That is what makes retargeting possible (you look at a product, you see an ad for it elsewhere), along with cross-site frequency capping and attribution.
Status: blocked by default in Safari since 2020 and Firefox since 2022. Still available in Chrome.
The cross-site recognition is both the reason they became central to digital advertising and the reason they attracted regulatory and browser scrutiny. A user visiting one site generally does not expect a company they have never heard of to recognise them on the next one.
Side by side
| First-party cookie | Third-party cookie | |
| Set by | The site you are visiting | Another domain embedded in the page |
| Main purpose | Logins, baskets, preferences, analytics | Cross-site recognition, retargeting, attribution |
| Works across sites | No | Yes, by design |
| Safari / Firefox | Works | Blocked by default |
| Chrome | Works | Works |
| Part of “cookieless” | No | Yes — this is the one people mean |
What actually happened to third-party cookies
This is where most explanations are now out of date, so it is worth being precise.
- 2020: Safari blocks third-party cookies by default. 2022: Firefox follows.
- 2020: Google announces it will phase them out of Chrome, then delays repeatedly.
- July 2024: Google abandons the plan. Third-party cookies stay in Chrome.
- April 2025: Google confirms it will not show a standalone cookie choice prompt either.
- 17 October 2025: Google retires most Privacy Sandbox APIs — the replacement technology — including Topics, Protected Audience and Attribution Reporting.
So third-party cookies did not disappear. They remain available in Chrome, with no end date, and the replacement that was being built for them has been shut down.
Why “cookieless” still matters anyway
Here is the part that surprises people: none of the above made the problem go away.
Safari and Firefox still block third-party cookies, and they always will. Mobile apps never used cookies at all — they relied on mobile advertising IDs, which Apple’s App Tracking Transparency restricted in 2021. Connected TV never had either. Taken together, more than 40% of web and mobile traffic now sits in environments where no traditional identifier is available.
That is why the industry still talks about cookieless advertising in 2026. The deadline was cancelled; the gap was not. If anything the position is harder than before, because there is no longer a platform-led replacement in development.
What this means if you buy or sell advertising
For publishers: impressions that reach the auction without an identifier attract fewer bidders and sell for less than equivalent cookied inventory. Our cookieless monetization guide covers how that gap is closed.
For advertisers: a significant share of your audience — concentrated on iOS, apps and CTV — cannot be targeted or attributed through cookies, and often goes under-counted as a result. Our page on Cookieless Audience Activation covers the advertiser side.
For everyone else: blocking third-party cookies in your browser settings is a reasonable privacy choice and will not break the sites you use. First-party cookies, the ones that keep you logged in, are unaffected.
For the full picture, read our guide to cookieless advertising.
FAQs
What is the main difference between first-party and third-party cookies?
Who sets them. A first-party cookie is set by the website you are visiting and is used for things like logins, baskets and preferences. A third-party cookie is set by a different domain embedded in that page, and is used to recognise the same person across different websites for retargeting, frequency capping and attribution.
Are first-party cookies being blocked too?
No. No major browser blocks first-party cookies by default and none plans to. Blocking them would log users out on every page and break ordinary site functionality. When people say “a cookieless future”, they mean third-party cookies only.
Are third-party cookies gone?
Not in Chrome. Safari has blocked them by default since 2020 and Firefox since 2022, but Google abandoned Chrome deprecation in July 2024 and ruled out a choice prompt in April 2025. They remain available in Chrome with no end date.
Is it safe to block third-party cookies in my browser?
Yes. Sites you use will continue to work, because logins and preferences rely on first-party cookies. You will mainly see less personalised advertising. Safari and Firefox already block them for you by default.
If cookies are staying in Chrome, why does cookieless advertising still matter?
Because Chrome was never the whole internet. Safari and Firefox still block third-party cookies, mobile apps never used them, and connected TV never had any shared identifier. More than 40% of web and mobile traffic sits in those environments, and Google retired most of the Privacy Sandbox in October 2025, so no replacement is coming.
What replaces third-party cookies for advertising?
No single thing. Most advertisers and publishers combine first-party data, contextual targeting and identity resolution — the last being the only approach that restores addressability across cookieless browsers, mobile apps and CTV without requiring users to log in.