Tag Management Systems (TMS) provide a centralized, rules-based container that controls when and how third-party tracking scripts and marketing pixels fire across web and mobile properties — without requiring direct code changes from engineering teams. Core capabilities include a tag library with vendor templates, a data layer abstraction, conditional firing rules, version control with publish/rollback, server-side tagging for first-party data control, and consent management integrations for GDPR/CCPA compliance. The market is dominated by Google Tag Manager, with enterprise alternatives (Tealium iQ, Adobe Experience Platform Tags, Piwik PRO, Commanders Act, Matomo Tag Manager).