Data & identity · also called EUID
European Unified ID (EUID)
European Unified ID (EUID) is the European version of Unified ID 2.0, an email-based, hashed and encrypted advertising identifier designed to work within GDPR's consent requirements.
EUID follows the same idea as Unified ID 2.0: turn a user's email address into a pseudonymous, encrypted identifier that publishers can pass to advertisers in place of cookies. It was set up by The Trade Desk specifically for Europe and the UK, where GDPR and ePrivacy rules require clear consent for most advertising uses of personal data.
The main differences are about consent and control. EUID is designed to be used when a user has given consent, typically captured through a CMP and signalled through the IAB TCF, and it runs on separate infrastructure with its own opt-out and transparency pages. Data is not supposed to be mixed with the US UID2 system.
Like UID2, EUID remains personal data under GDPR, because it can single out a person. Its reach depends on logins and consent rates, which vary by country and publisher. It is one of several email-based identity approaches competing in Europe alongside publisher and telecom-based IDs.
Think of it like this
EUID is like the same festival wristband scheme as UID2, but with a stricter door policy where you must explicitly agree before getting the band.
An example
A German publisher offers EUID to readers who log in and consent via its CMP; about 12% of impressions carry an EUID token, which buyers can use for frequency capping.
Related terms
Unified ID 2.0 (UID2)
Unified ID 2.0 (UID2) is an open-source advertising identifier, originally developed by The Trade Desk, generated from a user's hashed and salted email address or phone number with their consent.
GDPR
The GDPR (General Data Protection Regulation) is the European Union's data protection law, applying since May 2018, which governs how organisations collect and use personal data about people in the EU.
IAB TCF (Transparency & Consent Framework)
The IAB TCF (Transparency & Consent Framework) is IAB Europe's standard for collecting users' GDPR consent and objections through CMPs and passing those choices to ad tech vendors in a consent string.
Hashed email
A hashed email is an email address transformed by a one-way cryptographic function, usually SHA-256, into a fixed string used to match users across systems without sharing the plain address.
Consent string
A consent string is a compact encoded value recording a user's privacy choices, such as the TCF TC String or a GPP string, that travels with ad requests to vendors.
Sources: European Unified ID, General Data Protection Regulation (EU) 2016/679, EUR-Lex