What Is Cross-Domain Tracking?

Cross-domain tracking links a single user's activity across two or more different domains, for example a marketing site and a separate checkout domain, so that analytics and conversion tracking recognize the visit as one continuous journey rather than as two unrelated, disconnected sessions.

Without cross-domain tracking configured correctly, a customer who browses on a marketing site and checks out on a separate domain gets split into two sessions in analytics, inflating bounce rate, undercounting conversions, and muddying attribution since the two sessions look like two different visitors instead of one continuous journey. Getting it right requires passing identifiers correctly through the Data Layer and verifying tags on both domains fire consistently: exactly the kind of multi-page behavior manual GTM Preview Mode review struggles to catch.