What is UID2?

UID2 stands for Unified ID 2.0, an advertising identity framework that enables participating publishers, advertisers and technology providers to recognise matching identifiers without relying on third-party cookies. It uses email addresses or phone numbers as inputs to generate advertising identifiers.

Two terms are useful when understanding the system:

• A raw UID2 is an identifier derived through the framework’s processing.

• A UID2 advertising token is an encrypted form used in advertising workflows.

The official UID2 identifier documentation explains this distinction. An advertising token is not simply the original email address, and it is not interchangeable with a basic email hash.

UID2 also provides an opt-out mechanism. However, encryption and opt-out controls do not make identifiable advertising activity automatically anonymous or lawful. Participants still need appropriate disclosures, permissions where required and handling of user choices.

Understanding tokenization in privacy helps explain how protected identifiers can reduce direct exposure while still enabling records to be linked. UID2 should therefore be assessed as an identity system, not as a guarantee that personal data is no longer involved.