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The Madison Avenue Field GuideA field guide to marketing & advertising, by Brandon Mina

GlossaryPrivacy & IdentityThird-Party Data

Privacy & Identity

Third-Party Data

Data collected by companies with no direct relationship to the consumer and sold to others.

By Brandon MinaCEO, BrandPilot AIUpdated November 2026

Appears in Lesson 6 of Programmatic 101

Short answer

Third-party data is information collected by companies with no direct relationship to the consumers it describes, then aggregated and sold to other businesses. It typically comes from many sources and is packaged into audience segments by data brokers. Privacy regulations, consent requirements, and cookie restrictions have reduced its availability, accuracy, and appeal for advertisers.