What is Unified ID 2.0 (UID2)?
Unified ID 2.0 (UID2) is an open-source identity framework, led by The Trade Desk, that creates a privacy-focused ad identifier from an email address or phone number. When a user logs in to a participating site or app, their contact detail is hashed and turned into an encrypted token used for targeting and measurement instead of third-party cookies.
It is one of the best-known alternative IDs for the open internet, alongside publisher and platform login IDs.
How UID2 works
Login: a user signs in to a publisher site, app or streaming service with an email or phone number and is told how the data will be used.
Hashing and ID creation: the email or phone number is normalized and hashed, then a UID2 operator turns it into a raw UID2 using a secret salt.
Encryption: the raw UID2 is encrypted into a UID2 token, which the publisher passes in bid requests. Tokens are refreshed regularly, so the value in the bid stream keeps changing.
Decryption by participants: authorized DSPs and data partners that have agreed to the UID2 participation terms can decrypt the token and match it with their own audiences.
Opt-out: users can opt out through a public portal, and participants must honor that choice.
Advertisers can also convert their own customer emails into UID2s to build audiences, which makes first-party lists usable across publishers that support the framework. A sister framework, EUID, is designed for Europe and its consent requirements.
Why UID2 matters
Many impressions have no usable third-party cookie: Safari, Firefox, most apps and CTV environments. UID2 gives advertisers a persistent, people-based ID in those places, as long as users are logged in.
Addressability: targeting and frequency capping work wherever the same login is used.
Cross-device reach: because it is based on an email or phone number, the same ID supports cross-device targeting from phone to laptop to TV.
Measurement: exposure can be matched to conversions without relying on cookies.
User controls: consent and a central opt-out are built into the framework.
The limitation is scale. UID2 only exists for users who log in with an email or phone number on participating properties, and adoption differs by DSP, publisher and region.
UID2 vs third-party cookies
A third-party cookie is set by a domain the user is not visiting, is tied to one browser, and often has no clear login or consent step. UID2 is created from data the user actively provided, works across devices and environments including apps and TV, and comes with an opt-out. Both help recognize users across sites, but UID2 depends on authenticated traffic, so it typically covers fewer users with higher match quality.
UID2 with AdGeeks
Identity support differs by platform, so AdGeeks plans cookieless targeting around what each DSP offers. On DV360, Amazon DSP and Adform, our traders combine first-party data, contextual signals and the ID solutions each platform supports to keep reach and measurement steady as cookie coverage shifts.
