Enhancing identity at scale with ID5

Editor’s note: This article was originally published on July 6, 2023, and was updated on September 2, 2026, to reflect changes in the industry, including developments related to third-party cookie deprecation.

Enhancing identity at scale with ID5 

A privacy-conscious path to reach and relevance in Europe 

As privacy rules tighten, consumer expectations evolve, and signal loss grows, marketers need durable, privacy-aligned ways to reach audiences. 

That’s why The Trade Desk partnered with ID5, one of Europe’s leading identity providers. This integration helps advertisers go beyond legacy signals by unlocking a wide range of identity solutions tailored to regional privacy requirements, including probabilistic IDs that scale across cookie-free browsers, cross-device extension and frequency control, and publisher authentication with European Unified ID (EUID). 

Why ID5 matters 

Europe needs its own identity approach. With unique regulations and diverse markets, advertisers can’t rely on a one-size-fits-all solution. 

By integrating with Identity Alliance, our cross-device graph consisting of leading identity graph providers, ID5 enables marketers to connect publisher inventory, advertiser audiences, and consumer devices more precisely. 

ID5 offers two key tools: 

• A graph that supports identity resolution in signal-restricted browsers like Safari and Firefox, boosting addressability by up to 20% 

• The ID5 ID, a probabilistic identifier built on soft signals like IP and user agent, enabling cross-browser and cross-device reach 

Advertisers can rely on these tools to extend audience connection, improve ad relevance, and respect user privacy. 

How ID5 fits into the future of identity  

ID5 and ID5 ID are already widely adopted across Europe, where publishers are leaning into the value exchange of the open internet to support addressability. 

The Trade Desk’s integration with ID5 enables publishers using ID5 to more easily create EUIDs for authenticated users while still leveraging ID5 for unauthenticated user sessions. For advertisers, this integration supports the activation of audiences across a wide range of environments, regardless of whether users are authenticated. 

ID5 offers a flexible identity that allows marketers to maintain precision and amplify reach across browsers and formats, all while remaining aligned with European privacy standards. 

What’s next 

At The Trade Desk, we believe that no single ID will rule digital advertising. That future will be built on interoperable, privacy-conscious IDs rather than on outdated, one-size-fits-all solutions. 

Our partnership with ID5 is just one step toward creating a smarter identity future. 

Want to learn more about what’s next for identity? Discover how to make the most of first-party data in Europe.