A third-party cookie is a small file placed in your browser by a domain other than the one you're visiting, which for years allowed advertising companies to track the same user across completely different websites, building a profile of their interests to show more relevant ads. Safari and Firefox have blocked them by default for years, and Chrome, with the largest market share, has moved in the same direction, which in practice closes the main door on a technique that propped up a large part of digital advertising for two decades.
Why this especially affects remarketing
Classic remarketing (showing an ad to someone who already visited your site, while they browse other pages) relied heavily on third-party cookies to identify that user outside your own domain. Without them, the ability to track a user that precisely across different sites is considerably reduced, forcing ad platforms to develop alternative methods, generally less precise at the individual level but more respectful of privacy.
What's taking its place
First-party data, meaning the information you collect directly from your own customers (email after a purchase or sign-up, browsing history within your own site), becomes far more valuable because it doesn't depend on third-party cookies to work. Cohort-based targeting models (grouping users with similar interests without identifying each specific individual) are also growing, aiming for a balance between ad relevance and user privacy.
What your business can do to adapt
Prioritise collecting first-party data directly: newsletters, customer accounts, loyalty programmes, any mechanism that lets you identify and contact your customers without relying on third parties. Invest in content and SEO, channels that never depended on third-party cookies to work and that gain relative weight in an ecosystem where remarketing becomes less precise. And review how your ad platform measures your conversions, because attribution models are also changing to adapt to this new scenario with less cross-site tracking data available.
What doesn't change
First-party cookies, the ones placed directly by the domain you're visiting for basic functions like keeping you logged in or remembering a shopping cart, aren't affected by these changes. Confusion between the two cookie types is common, and it's worth being clear on it so you don't overreact by removing your own site's functionality that was never actually at risk.
Frequently asked questions
Does my website stop working without third-party cookies?
No, your own site's basic functions (login, cart, preferences) rely on first-party cookies, not third-party ones, so they keep working normally. What's mainly affected is advertising and tracking across different domains.
Should I stop investing in remarketing?
Not necessarily, but expectations should be adjusted: remarketing still works, though with less precise cross-site targeting than a few years ago, and increasingly supported by first-party data rather than third-party cookies.
What can I do right now to prepare?
Starting to actively build your own customer database (email, behaviour on your site), instead of relying entirely on external ad platforms to reach your audience, is the most practical move with the biggest medium-term impact.