For roughly three decades, the humble cookie quietly held the web together: it kept you logged in, remembered your shopping cart, and let advertisers follow you from site to site. That last job is the one that’s now coming apart. Privacy regulation, browser blocking, and Google’s own roadmap have turned “the cookie” from a marketer’s default into something you have to think carefully about. If you run digital campaigns, you can’t afford a fuzzy understanding of what a cookie actually is and which kind is going away.
What a cookie actually is
A cookie is a small text file a website asks your browser to store. The next time your browser talks to that site (or, in some cases, another site), it sends the cookie back. That round trip is what lets a website “remember” you between page loads and visits. A cookie is not a program, it can’t execute code, and it can’t read files off your computer. It’s just a labeled note your browser holds and hands back when asked.
The single most important distinction in modern marketing isn’t session vs. persistent (more on that below) but who set the cookie: the site you’re actually visiting, or a third party riding along in the background.
First-party vs. third-party cookies
A first-party cookie is set by the domain in your address bar. When you log into a retailer and it keeps you signed in, that’s a first-party cookie doing exactly what cookies were designed to do. These are useful, generally trusted, and not going anywhere.
A third-party cookie is set by a different domain than the one you’re visiting, usually an ad network or tracking script embedded in the page. Because the same network is embedded across thousands of sites, it can stitch together a profile of where you’ve been. That cross-site tracking is what powered classic retargeting and a lot of audience-based ad buying, and it’s also what privacy advocates and regulators have spent years pushing back against.
From our agency experience, the clients who get blindsided are the ones who assumed all their tracking was equally durable. The reckoning lands almost entirely on the third-party side.
The third-party cookie deprecation, accurately
Here’s where you need precision, because a lot of outdated advice is still floating around. Apple’s Safari has blocked third-party cookies by default since 2020, and Mozilla’s Firefox has done the same for years. So for a meaningful slice of traffic, third-party cookies have already been gone for a long time.
Google Chrome, the browser with the largest share, was the holdout. Google spent years promising to phase out third-party cookies in Chrome, pushing the deadline back repeatedly. Then in 2024 it changed course: rather than killing third-party cookies outright, Google said it would instead give Chrome users a choice about them through a prompt, and in 2025 it confirmed it would not roll out a standalone deprecation prompt, leaving the existing controls in place. The practical upshot: third-party cookies still technically work in Chrome today, but their long-term reliability is anything but guaranteed, and they’re already blocked on Safari and Firefox.
What we consistently see is that “are third-party cookies dead?” is the wrong question. The right framing is: they’re unreliable, partially blocked, and not something to build a strategy on. First-party data is the foundation that holds.
Session vs. persistent cookies
A second, more technical distinction is how long a cookie lasts:
- Session cookies live only until you close the browser. They handle short-term jobs like keeping items in a cart while you shop.
- Persistent cookies carry an expiration date and survive across visits. They’re what remember your preferences or keep you logged in next week.
This is independent of the first-party/third-party split: you can have a persistent first-party cookie (your saved login) or a persistent third-party cookie (the old tracking workhorse).
What this means for your marketing
When we run campaigns for clients, the cookie shift shows up in a few concrete ways. Audience-based retargeting that leans on third-party cookies reaches fewer people and reports less accurately than it used to. Conversion measurement gets murkier as browsers cap cookie lifetimes. And consent banners are no longer optional in markets covered by laws like the GDPR and ePrivacy rules in Europe.
The teams adapting well are doing three things: investing in first-party data they collect with clear consent, leaning on server-side and consent-mode measurement to fill measurement gaps, and treating contextual targeting (matching ads to page content rather than to a tracked individual) as a real channel again rather than a fallback. None of this requires abandoning paid media. It requires not treating the third-party cookie as load-bearing.
Frequently asked questions
Are cookies dangerous?
A cookie itself can’t run code or carry malware. The legitimate concern is privacy: third-party cookies can track behavior across many sites. You can clear or block cookies in any browser’s settings, and you can block third-party cookies specifically without breaking most first-party functionality.
Will first-party cookies be affected too?
The deprecation conversation is about third-party cookies. First-party cookies, the ones that keep you logged in and remember your cart, are not being phased out. Browsers do increasingly cap how long they persist, but the mechanism stays.
Do I still need a cookie consent banner?
If you reach users in jurisdictions with laws like the EU’s GDPR, yes, and you generally need consent before setting non-essential cookies. Even outside those markets, a clear consent flow is fast becoming a baseline expectation.
What replaces third-party cookies for advertising?
There’s no single drop-in replacement. The practical mix is first-party data, contextual targeting, privacy-preserving measurement (like consent mode and server-side tagging), and platform-native audiences where the platform handles the data.
Related terms
- First-party data — information you collect directly from your audience with consent; the strategic answer to cookie loss.
- Retargeting — re-engaging past visitors, historically powered by third-party cookies and most affected by their decline.
- GDPR — the EU privacy law that made cookie consent a legal requirement, not a courtesy.
- Pixel (tracking pixel) — a tiny image used alongside or instead of cookies to record that an action happened.
- Organic traffic — visits you earn without paid placement, an audience source that doesn’t depend on cookie-based ad targeting.
