The essentials
- Definition: a third-party cookie is set by a domain other than the site being visited, which makes it possible to follow a user from one site to another.
- Uses: remarketing, cross-site conversion measurement, frequency capping, advertising audiences, multi-touch attribution.
- Where things stand in 2026: blocked by default on Safari since 2020 and Firefox since 2019; Google gave up removing them from Chrome in 2024 and now offers users a choice.
- Replacements: first-party data, server-side tracking, conversions APIs, modelling, contextual targeting and consented identifiers.
A third-party cookie is a file set in the browser by a domain other than the site being visited. When someone visits an online store carrying an advertising tag, it is the ad platform that sets the cookie, not the retailer. Because that cookie is readable on every site using the same platform, it allows the same person to be recognised from one site to the next: it is the technical foundation of the last twenty years of targeted advertising. It stands in contrast to the first-party cookie, set by the site itself to remember a session or a preference.
What third-party cookies were for
| Use | What it allowed | Impact of its disappearance |
|---|---|---|
| Remarketing | Retargeting a visitor on other sites | Smaller audiences, shorter retention windows |
| Conversion measurement | Connecting an ad click to a purchase made later | Unattributed conversions, understated ROAS |
| Frequency capping | Limiting how often one person sees an ad | Repetition poorly controlled, budget wasted |
| Behavioural audiences | Targeting by the sites someone has visited | Targeting refocused on context and first-party data |
| Multi-touch attribution | Following a journey across several sites | Last-click or modelled attribution; see data-driven attribution |
Where their disappearance stands in 2026
Safari has blocked them by default since 2020 with intelligent tracking prevention, Firefox since 2019. Google announced their removal from Chrome several times between 2020 and 2024, then reversed course in July 2024: rather than removing them, Chrome now offers users a choice, and the Privacy Sandbox has not replaced classic targeting as planned. In practice, roughly half of European web traffic already flows without a usable third-party cookie, and consent refusals remove a further share. Their disappearance is therefore not a coming event but a continuous erosion: advertisers who were waiting for a deadline lost time, those who built up their first-party data got ahead.
What to replace them with
- First-party data: email addresses, customer accounts, purchase histories collected with consent; that is the foundation, set out in first-party data.
- Server-side tracking and conversions APIs: sending conversions from the site's server rather than from the browser, described in CAPI.
- Modelling: the statistical estimation of unobserved conversions, enabled by Consent Mode at Google.
- Contextual targeting: delivering ads according to the content of the page rather than the person's history; it is coming back strongly and avoids any question of consent.
- Consented identifiers: hashed email addresses, used for customer lists and lookalike audiences, within the bounds of the consent collected.
- SEO and GEO: organic visibility depends on no cookie at all, and mechanically gains in relative value.
What it changes in practice for a small business
Three effects are already visible. Remarketing audiences are shrinking: a 30-day visitor list has lost 30 to 50% of its volume compared with 2021. The conversions platforms report are drifting away from real sales, which means reading your results in GA4 or your CRM rather than in Meta Ads or Google Ads. And the value of a consented contact base is rising: an identified customer can be retargeted, excluded and used to build lookalike audiences, where the cookie no longer allows it. Customer lists feed lookalike audiences.
How GreenRed helps
Rather than juggling several tools, GreenRed's SMO and SMA social media tracking brings these metrics together in a single dashboard, compares them over time and tells you which actions come first. You can try it free, with no card, from the Pricing.
Frequently asked questions
What is a third-party cookie?
A cookie set in the browser by a domain other than the site being visited, generally an advertising platform. Readable on every site using the same platform, it allows a user to be recognised from one site to the next, and underpins classic targeted advertising.
Have third-party cookies disappeared in 2026?
Not entirely. Safari and Firefox have blocked them by default since 2019 and 2020, but Google gave up removing them from Chrome in 2024 and now offers users a choice. In practice about half of European traffic already flows without a usable third-party cookie, and consent refusals reduce the remaining share further.
What is the difference between a third-party and a first-party cookie?
A first-party cookie is set by the site being visited, to remember a session, a basket or a preference; it remains largely functional. A third-party cookie is set by another domain and serves cross-site tracking; that is the one browsers block.
What should replace third-party cookies?
First-party data collected with consent, server-side tracking and conversions APIs, modelling of the missing conversions, contextual targeting, consented identifiers such as hashed emails, and a greater share of organic visibility.