Browser tracking isn't one technique — it's a layered ecosystem of methods that have evolved partly in response to earlier defenses, meaning understanding the full picture requires looking at several distinct mechanisms together.
First-party vs. third-party cookies
A first-party cookie is set by the site you're actually visiting; a third-party cookie is set by a different domain embedded within that page (commonly an advertising or analytics provider), letting that third party potentially track you across many different sites that all embed its content.
Tracking pixels
A tiny, often invisible image loaded from a tracking server, whose mere request (regardless of whether the image itself does anything visible) confirms to the tracker that a specific page was loaded — commonly used in email tracking and web analytics.
Link decoration
Some tracking appends identifying parameters directly to URLs (link decoration) rather than relying on cookies at all, letting a tracker follow a click's origin and destination even when cookie-based tracking is blocked.
Storage APIs beyond cookies
Modern browsers offer several storage mechanisms beyond traditional cookies — local storage, IndexedDB, and others — some of which have historically been used for tracking purposes that persist even when cookies specifically are cleared or blocked.
Fingerprinting as a cookie-independent fallback
As cookie-based tracking has faced increasing restriction, fingerprinting (see Browser Fingerprinting) has become a more prominent fallback specifically because it doesn't rely on anything stored that can be cleared.
FAQ
Does blocking third-party cookies stop tracking entirely?
No — it addresses one specific mechanism; link decoration, fingerprinting, and first-party tracking (where the site you're visiting itself tracks you, not a third party) all remain unaffected by third-party cookie blocking alone.