A small data file stored in a consumer's web browser that records their interaction with an affiliate publisher's link, used to attribute subsequent purchases to the correct publisher for commission payment. Tracking cookies are the traditional mechanism for affiliate conversion attribution, though server-to-server (S2S) tracking is increasingly used alongside or instead of cookies. How tracking cookies work in affiliate: consumer clicks an affiliate link; the affiliate network's tracking system fires and places a cookie in the consumer's browser containing the publisher's ID, a click timestamp, and a unique click identifier; the cookie persists in the browser for the duration of the cookie window (typically 30, 60, or 90 days); if the consumer purchases within the cookie window, the tracking pixel or script on the brand's order confirmation page reads the affiliate cookie and fires a conversion event to the network; the network records the conversion and credits commission to the publisher identified in the cookie. Cookie window: the cookie window (also called attribution window or cookie duration) defines how long after a click a purchase can be attributed to the publisher; a 30-day cookie window means purchases that occur within 30 days of the affiliate click are credited to that publisher; longer cookie windows are more favorable to publishers because they allow credit for purchases that occur after longer consideration periods. Tracking cookie limitations: consumers who clear their browser cookies between clicking and purchasing lose attribution; Safari's Intelligent Tracking Prevention (ITP) limits cookie lifetimes to 24 hours, significantly reducing effective cookie windows for Safari users; browser extensions (ad blockers, privacy tools) may block or delete affiliate cookies; cross-device tracking is not possible with cookies (mobile click, desktop purchase). These limitations are why S2S postback tracking is increasingly implemented alongside cookie tracking.
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