So the question becomes, “How do you reliably target audiences across multiple devices when cookies don’t work?”
Well, two main ways have evolved: Probabilistic Models and Deterministic IDs. And while they both (sort of) solve the same problem, the way they do it is as different as old bunny ears antennae and cable.
WTF is Cross-Device Tracking – Digiday
A Marketer’s Guide To Cross-Device Identity – AdExchanger