The deprecation of the third-party cookie has been the most consequential technical transition in digital advertising in a decade. The cookie — a small data file placed on a user’s browser by a third-party domain — was the foundational mechanism through which the programmatic advertising ecosystem tracked users across websites, built audience segments for targeting, and measured the effectiveness of advertising campaigns. As browser changes and privacy regulations have eroded this mechanism, the entire AdTech industry has been forced to rethink how identity works in digital advertising. The solutions being built in response represent one of the defining investment areas of the current phase of the $869 billion global AdTech market.
How Third-Party Cookies Worked
For most of the programmatic advertising era, the third-party cookie was the invisible infrastructure that made targeted digital advertising possible. When a user visited a website, third-party scripts — from ad servers, data management platforms, and analytics tools — placed small data files in the user’s browser. These files contained identifiers that persisted across sessions, allowing the same user to be recognised across different websites.
This recognition enabled the core functionality of audience-based advertising: an advertiser could identify users who had visited their website, build lookalike audiences from their customer data, and exclude existing customers from acquisition campaigns. Data management platforms assembled audience segments from cookie-based user data and made these segments available to DSPs for campaign targeting. Attribution systems matched ad impressions to conversions by tracking users across the journey from ad exposure to purchase.
The Erosion of the Cookie
The deprecation of third-party cookies did not happen in a single moment. It was a gradual process driven by both regulatory action and platform-level decisions. Apple’s Safari browser introduced Intelligent Tracking Prevention (ITP) in 2017, which substantially restricted the lifespan and functionality of third-party cookies. Mozilla’s Firefox adopted similar restrictions. By the time Google announced that Chrome would phase out third-party cookie support — a decision that has been delayed multiple times and remains ongoing — the effective reach of third-party cookie-based targeting had already been significantly diminished in Safari and Firefox.
GDPR in Europe and CCPA in California added a consent layer on top of the technical restrictions, requiring that users explicitly consent to data collection for advertising purposes. In markets with high GDPR compliance rates, the proportion of the audience available for cookie-based targeting has been substantially reduced even in browsers that still support third-party cookies.
Universal ID Solutions
The industry’s primary response to the deprecation of third-party cookies has been the development of universal ID frameworks — standardised identifiers that can function as replacements for the cookie in the open web programmatic ecosystem.
The Trade Desk’s Unified ID 2.0 (UID 2.0) is the most widely adopted of these frameworks. UID 2.0 works by hashing email addresses or phone numbers — data that users provide when they register or log in to publisher websites — to create a persistent, privacy-compliant identifier that can be used for targeting and measurement across participating publisher and platform partners. LiveRamp’s RampID operates on a similar principle, using authenticated user data as the basis for a cross-site identifier.
Contextual Targeting: The Privacy-Native Alternative
Contextual targeting — serving ads based on the content context of the page rather than inferred user attributes — has experienced a significant revival as cookie-based targeting has declined. Modern contextual targeting has been substantially enhanced by natural language processing and AI, enabling much more nuanced content classification than the keyword-matching approaches that characterised early contextual advertising. Platforms including Integral Ad Science and Proximic by Comscore now offer AI-powered contextual targeting that can classify content at the paragraph level and predict audience receptivity from content signals without any user tracking.
First-Party Data as the New Currency
The most durable solution to cookie deprecation is first-party data — information that users provide directly to publishers and advertisers, collected with explicit consent and stored in the collecting organisation’s own systems. First-party data is not affected by browser restrictions or third-party cookie deprecation because it does not depend on cross-site tracking.
For publishers, building first-party data assets means investing in authenticated experiences — registration walls, subscription models, personalisation features that encourage login — that give users reasons to share their data. For advertisers, first-party data activation means connecting their CRM data, purchase history, and subscriber information to programmatic buying through clean room environments. The CDP market has grown substantially as a result of increased demand for platforms that can manage, unify, and activate first-party data for both marketing and advertising purposes.
Privacy Sandbox and the Browser-Level Alternative
Google’s Privacy Sandbox initiative proposed a browser-level alternative to third-party cookies — a set of APIs built into the Chrome browser that would allow advertising use cases to be performed within the browser, without user-level data leaving the device. The Protected Audience API and the Topics API are the primary advertising-relevant components of the Privacy Sandbox. Adoption among AdTech platforms has been mixed, and the timeline for Chrome’s cookie deprecation has been revised multiple times, leaving the industry operating across a mix of approaches simultaneously.
The Identity Landscape in 2026
The digital advertising identity landscape in 2026 is more fragmented than it was in the cookie era, but also more robust in important ways. Advertisers must now operate across a portfolio of approaches — authenticated first-party data in environments where users have logged in, universal IDs where publishers have built authentication infrastructure, contextual targeting for anonymous inventory, and modelled approaches for environments where no direct targeting signal is available.
This complexity has driven investment in identity resolution technology that can manage and reconcile signals across these different approaches. The transition from the cookie era to the multi-signal era has added substantial complexity to advertising technology operations — and that complexity, measured in investment required to navigate it, is one of the factors sustaining the 9.8% annual growth rate of the global AdTech market.
