Identity resolution is the process of connecting fragmented data points, email addresses, device IDs, IP addresses, login data, cookie IDs, behavioural signals, into a single unified profile representing one real person. In digital advertising, it’s the technology that lets a brand recognise the same user whether they’re browsing on a work laptop, tapping on a personal phone, watching connected TV in the living room, or visiting a physical store. Without identity resolution, those touchpoints look like four different people.
Identity resolution operates through two core approaches that are often used together: deterministic matching and probabilistic matching.
Deterministic matching ties signals to a confirmed, persistent identifier, most commonly a hashed email address collected when a user logs in, makes a purchase, or submits a form. Because it’s anchored to a known identity event, deterministic matching is highly accurate. The limitation is reach: you can only match users who have shared a verifiable identifier at some point.
Probabilistic matching uses statistical modelling to infer that multiple signals likely belong to the same person, based on shared attributes: overlapping IP addresses, similar browser fingerprints, consistent geographic patterns, or shared device usage timing. Probabilistic matching extends reach beyond confirmed logins but introduces a margin of error that deterministic avoids.
The output of both approaches is an identity graph, a persistent map of which signals and devices belong to which individual or household. This graph is what advertisers and DSPs use to target, frequency-cap, and measure campaigns across channels. Major identity frameworks in active use include LiveRamp RampID, The Trade Desk’s Unified ID 2.0 (UID2), and ID5.
With third-party cookies deprecated in Safari and Firefox and restricted in Chrome, identity resolution has become the primary mechanism for cross-channel targeting and multi-touch attribution. IAB Europe reports that 51% of addressability solutions in 2026 depend on unified ID frameworks rather than cookies.
For publishers, participating in identity resolution networks directly affects CPMs. Addressable inventory, where the buyer can confirm who they’re reaching commands significantly higher rates than anonymous inventory. Publishers who collect first-party data through newsletters, account sign-ups, or gated content and activate it through an identity framework are in a fundamentally stronger monetisation position than those relying entirely on contextual signals.
For advertisers, identity resolution enables the frequency control, sequential messaging, and cross-device attribution that modern campaign management requires. Without it, the same user can be shown the same ad 20 times across different devices while the campaign reports just 2 impressions per person.