Cookies are small text files stored on a user's browser when they visit a website. They allow the website - and third-party services embedded within it - to remember information about the user between sessions: their login status, cart contents, language preferences, and browsing behaviour. For e-commerce and digital advertising, cookies have historically been the primary mechanism for user identification, behavioural tracking, and ad targeting across the web.
There are two types of cookies with distinct roles. First-party cookies are set by the website the user is visiting. They are used for core site functionality - keeping items in a cart, maintaining a logged-in session, remembering preferences - and for analytics tools like Google Analytics that measure on-site behaviour. First-party cookies are generally not subject to the same restrictions as third-party cookies. Third-party cookies are set by external domains embedded in a page - advertising networks, social media pixels, analytics services. They enable cross-site tracking: a cookie set by Meta's pixel on one website can identify the same user on another website, enabling retargeting across the web and building cross-site behavioural profiles for ad targeting.
Third-party cookies are being phased out. Safari and Firefox have blocked them by default for years; Google has been progressively restricting them in Chrome. Apple's App Tracking Transparency (ATT) framework extended similar restrictions to mobile app tracking. These changes have significantly reduced the signal available for tracking pixel-based advertising and have been a primary driver of the shift toward first-party data and zero-party data collection as the foundation of personalisation and audience targeting.
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