Identity Resolution
Identity resolution is the cross-device, cross-platform stitching layer that lets advertisers and platforms recognize the same user across browsers, mobile, CTV, and email. It is the foundational layer for addressable targeting, attribution, and cross-screen measurement after the collapse of third-party cookies as the universal web identifier.
Identity resolution is the part of the ad stack that does not get a marketing campaign of its own and yet decides whether the rest of the stack works. It is the layer that answers a single question on every impression: is the person about to see this ad the same person we saw yesterday on a different device, in a different app, on a different network? For two decades the answer was a third-party cookie. The cookie was never a great identity signal, but it was a universal one. That is no longer true.
Safari and Firefox stripped third-party cookies out by default years ago. Chrome — the browser that carries roughly two-thirds of web traffic — spent seven years preparing a Privacy Sandbox replacement, then retired most of those APIs in October 2025 and reverted to a user-choice model that, in practice, leaves the cookie in a degraded, opt-out-prone state. The single web-wide identifier the industry was waiting for is not coming.
What replaced it is not one thing. It is a layered stack. Authenticated IDs — Unified ID 2.0 from The Trade Desk, RampID from LiveRamp, ID5 — operate where a publisher has a logged-in user and a hashed email to anchor on. Where there is no login, probabilistic graphs and contextual signals carry the impression. Inside the walled gardens — Amazon, Google’s PAIR, Apple’s AdAttribution Kit — first-party identity stays first-party and is reconciled with advertiser data inside a clean room rather than passed through the open bidstream. CTV runs on its own logic entirely: device graphs, IP households, ACR, and increasingly platform-native IDs after Roku standardized on UID2 across its premium inventory in December 2025.
The buyer’s mental model has shifted accordingly. The question is no longer “what is the universal ID?” — that fight is over and nothing won. It is “what is the right identity layer for this inventory, in this jurisdiction, against this measurement question?” The vendors that thrive in this market are the ones that interoperate cleanly across all of those answers; the ones that bet on a single ID winning are the ones repricing their roadmaps.