Identity resolution

Identity resolution is the process of linking the identifiers one person or household uses, such as emails, logins, cookies and device IDs, into one profile or ID for targeting, frequency control and measurement.

The IAB Tech Lab's clean room guidance lists identity resolution, or bridging, among core clean room functions. An identity partner creates a direct match between two or more datasets, with or without a shared key. It also describes crosswalk tables that map one identity space to another, for example LiveRamp RampID to Experian's ID (IAB Tech Lab, Data Clean Rooms Guidance, v1.0).

Links are either deterministic, based on a login or hashed email, or probabilistic, inferred from signals such as IP address and device type. OpenRTB lets the seller say which kind it used. In the extended ID object, mm value 3 means an authenticated match, 4 an observed first-party ID and 5 an inference across browsers or devices. The atype value 3 marks a person-based ID that is the same across devices (IAB Tech Lab, AdCOM 1.0).

Example: A CTV bid request carries the TV's advertising ID. The publisher also adds the ID of a phone it believes is in the same household, based on a shared IP address, with "mm": 5. A DSP can use the phone ID for frequency control but may decline to treat it as a confirmed person match.

Related terms: entity resolution, household graph, RampID, UID2, user matching, hashed email.

Authoritative source: IAB Tech Lab, "Data Clean Rooms Guidance and Recommended Practices", version 1.0 (2023), section 3 (GitHub, accessed 9 November 2026).

Read the full guide: Identity graph architecture for first-party data.