What are third-party cookies?

Third-party cookies are small pieces of data stored in a user’s browser by a domain different from the website the user is currently visiting. They have traditionally been used by advertising, analytics, and other third-party services to recognize users across different websites and support activities such as targeted advertising and measurement.

How Third-Party Cookies Work

For example, suppose a user visits an online store that contains an advertising or analytics service from another company. That third party may place a cookie in the user’s browser. If the user later visits another website that uses the same third-party service, the cookie may help the service recognize the browser across those sites.

Common Uses

• Cross-site advertising: Helping advertisers show relevant ads based on browsing activity.
• Ad measurement: Measuring whether users interacted with or converted after seeing an advertisement.
• Retargeting: Allowing advertisers to reach users who previously visited a website.
• Audience building: Helping create audience segments based on browsing behavior.
• Analytics: Supporting certain forms of cross-site measurement and attribution.
• Fraud prevention: Some third-party services use cookies to help identify suspicious activity.

Third-Party vs. First-Party Cookies

Privacy Considerations

Third-party cookies have raised privacy concerns because they can enable cross-site tracking and profiling. Privacy regulations and browser policies have therefore placed increasing restrictions on their use, leading advertisers to explore alternatives such as first-party data, contextual advertising, consent-based tracking, and privacy-preserving measurement.

In short: Third-party cookies are browser identifiers set by domains other than the website being visited, traditionally used for cross-site tracking, targeted advertising, retargeting, and measurement.