Privacy & Tech

What is Unified ID?

In digital advertising, a unified ID is a shared identity approach that helps participating systems recognise matching users or browsers. The name also refers to The Trade Desk’s original Unified ID solution, which should be distinguished from Unified ID 2.0, or UID2.

Term	What it refers to
Unified identifier	A general concept for linking identity across participating systems.
The original Unified ID solution	The Trade Desk’s earlier approach using its TDID identifier and cookie-based integrations.
UID2	A separate framework that derives identifiers from email addresses or phone numbers and supports encrypted advertising tokens.

The Trade Desk’s original Unified ID adoption guidelines describe the earlier implementation. For the newer framework, see how UID2 works.

The distinction matters when reading integration instructions or assessing a provider’s claims. “Unified” does not mean an identifier works everywhere, and a shared identifier is not automatically anonymous. Its privacy implications depend on what it links, who can use it and how user choices are respected.