What are third-party cookies?
Third-party cookies are small text files stored in a browser by a domain other than the website the person is visiting. They are typically set by ad tech companies through ads, pixels or embedded scripts, and they let those companies recognize the same browser across many sites. That makes them useful for retargeting, audience building, frequency capping and attribution.
A first-party cookie, by contrast, is set by the site you are actually on, for example to keep you logged in or remember your cart.
How third-party cookies work
You visit a news site that loads an ad or tracking pixel from an ad tech domain.
That ad tech domain sets a cookie with an ID in your browser.
Later you visit a different site that loads code from the same ad tech domain.
Your browser sends the same cookie back, so the company knows it is the same browser.
By joining these sightings, ad platforms can build audience segments, show retargeting ads, cap frequency across sites and connect impressions to conversions.
Where third-party cookies stand in 2026
Safari and Firefox: block third-party cookies by default through tracking protection features.
Chrome: Google spent several years planning to phase them out, then changed course. In 2025 it confirmed it would keep third-party cookies in Chrome and dropped the deprecation plan, leaving users with existing privacy controls.
Consent rules: privacy laws such as GDPR in Europe require consent for non-essential cookies, so in many markets a large share of users never allow them.
Apps and CTV: cookies do not exist in most mobile apps or on connected TVs, which use device IDs or other signals instead.
The practical result: third-party cookies still work in part of Chrome traffic, but they cover a shrinking, uneven share of the audience. Strategies that rely on them alone miss many people and give incomplete measurement.
Third-party vs first-party cookies
First-party cookies are set by the site the user visits and stay within that site. Browsers generally allow them, and they power logins, carts and on-site analytics. Third-party cookies are set by outside domains to follow users across sites, which is why browsers and regulators restrict them. For advertisers, the shift means relying more on first-party data collected with consent.
Alternatives to third-party cookies
Contextual targeting: target by page content rather than user history.
First-party data: customer lists and site audiences, activated through platform integrations.
Identity frameworks: email-based IDs such as UID2.
Platform signals: logged-in data from large platforms, such as Google and Amazon audiences.
Together these make up most cookieless advertising strategies.
Third-party cookies with AdGeeks
AdGeeks plans campaigns that do not depend on any single signal. On DV360, Amazon DSP and Adform, our traders combine platform audiences, your first-party data, contextual targeting and cookie-based segments where they still work. To get started, request access.
