Definition
An HTTP cookie is a small piece of data a website stores in the user's browser and that the browser sends back to that site on subsequent requests. Cookies let a site recognise a returning visitor, keep them logged in, remember preferences, and — in advertising — remember that a visitor arrived through a particular affiliate link so a later conversion can be attributed.
First-party cookies are set by the site the user is visiting; third-party cookies are set by other domains (typically ad and analytics services) embedded in the page.
Affiliate tracking has historically leaned on cookies: a click sets a cookie carrying the affiliate ID with an expiry equal to the attribution window, and if the user converts before the cookie expires, the sale is credited to that affiliate. The cookie lifetime — 7, 30, 90 days or longer — directly determines how much delayed conversion an affiliate gets paid for.
In context
Third-party cookies have been progressively restricted — blocked by default in several major browsers, limited by tracking-prevention features, and slated for deprecation more broadly — which breaks the classic third-party-cookie attribution chain. In response, iGaming affiliate tracking has shifted toward first-party cookies set by the affiliate's own tracker domain and, more importantly, toward server-to-server postbacks that pass a click ID and do not depend on the browser storing anything.
For an affiliate, the practical implications are: prefer programmes and trackers that support click-ID postback attribution over cookie-only tracking; understand that a brand's stated "cookie lifetime" may not be fully honoured in browsers that restrict cookies; and test the attribution end to end on the browsers the traffic actually uses, because a setup that works in one browser can silently fail in another. Cookies still matter for login state, consent records and first-party analytics, but as the sole basis for paying commissions they are no longer reliable.
Worked example
An affiliate notices its conversion count from one traffic source is 30% below the advertiser's — the source is mostly Safari users, where third-party cookies are blocked and the cookie-based fallback fails. Switching the programme to click-ID postback attribution, which does not use cookies, closes the gap.
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