The user permission required under GDPR and similar privacy laws before affiliate tracking cookies can be placed in a visitor's browser. Applies to: EU/UK visitors to websites with affiliate tracking; any brand whose affiliate program reaches EU/UK consumers must implement cookie consent for affiliate tracking cookies. Consent requirements: explicit opt-in (not pre-ticked boxes); informed (user understands what data is collected and why); granular (user can accept necessary cookies while declining marketing/tracking cookies); revocable (user can withdraw consent after giving it). Impact on affiliate attribution: users who decline cookie consent don't receive affiliate tracking cookies; their subsequent purchases aren't attributed to the publisher whose link they clicked (even if the click influenced the purchase); brands can estimate attribution loss from consent decline rates by tracking the gap between click volume and attributed conversions in EU/UK markets. Mitigation: server-side tracking (S2S postback) is less affected by cookie consent (attribution happens server-to-server rather than in the user's browser); cookieless attribution models use probabilistic methods to estimate publisher contribution without relying on cookies.
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