Zero-, first- and third-party data and what they really mean for marketing, analytics and compliance

For years, digital marketing was fueled by third-party data, information collected across websites and repackaged for targeting and analytics. This system enabled programmatic advertising at scale but relied on intransparent tracking practices.

That model started collapsing from the moment Google first announced the deprecation of third-party cookies, and has continued to do so, even beyond Google’s retraction. Safari and Firefox blocked third-party cookies through ITP and ETP years ago (Apple, 2017; Mozilla, 2019). Google Chrome, with around 65% global market share, began its phased deprecation in 2024 and expanded it in 2025 under the Privacy Sandbox (Google, 2024; StatCounter, 2025).

For businesses, this raises more than just compliance questions. It redefines data strategy. Companies now need to differentiate between:

• zero-party data: what customers willingly share,
• first-party data: what businesses collect through their own channels, and
• third-party data: what was once abundant but is rapidly disappearing.

The implications go far beyond advertising. For Marketing teams, the call is clear: rethink personalization when third-party audiences vanish. Analytics teams face challenges in attribution and measurement as long-standing tracking methods break down.

In this article, we will break down what zero-, first-, and third-party data actually mean, how they differ, and why these distinctions are now critical for anyone working in marketing, analytics, or compliance.

Data types and what they do

Zero-party data: intentionally shared by the user

Zero-party data is information that customers proactively and willingly provide to a company. It can include product preferences, communication choices, or answers to surveys and quizzes. Unlike other forms of data, it doesn’t need to be inferred or tracked, the user directly hands it over.

• Examples: a newsletter sign-up where users choose topics of interest, a preference center in an app, or a quiz that matches products to a user’s stated needs.
  
  
• Why it matters: it is both highly accurate (because it reflects real intentions) and highly consensual, aligning neatly with GDPR requirements around transparency and informed consent.
  

First-party data: collected directly by the company

First-party data refers to information a business collects through its own channels when users interact with its website, apps, emails, or physical stores. Unlike zero-party data, it is not always volunteered but results from customer behavior.

• Examples: website analytics (page visits, click paths), purchase history, CRM data, email engagement, or app usage patterns.
  
  
• Collection methods: often via first-party cookies, SDKs, server-side tracking, or loyalty program systems.
  
  
• Why it matters: first-party data is the backbone of modern analytics. It is reliable, under the company’s control, and future-proof compared to third-party data. However, it still requires consent in most jurisdictions if cookies or tracking technologies are involved.

Third-party data: aggregated and bought from elsewhere

Third-party data is collected by entities that have no direct relationship with the end user. This data is aggregated across websites or apps, bundled into audience segments, and sold for advertising or analytics purposes.

• Examples: audience segments purchased from a data broker, or third-party cookies that track user activity across multiple websites.
  
  
• Why it matters: third-party data once powered most programmatic advertising, enabling cross-site retargeting and large-scale audience expansion. But it is now in sharp decline, blocked by browsers and increasingly scrutinized by regulators. Its reliability is also questionable, since users rarely know who is collecting the data or how accurate it is.

How they differ in practice

While the three categories are often discussed together, their collection methods, reliability, ownership, and compliance implications are very different.

Collection mechanism

• Zero-party data is actively given by the user (e.g. survey responses, preference settings).
  
• First-party data is passively observed by the company during interactions (e.g. website visits, purchases).
  
• Third-party data is gathered indirectly by external actors, usually without a direct relationship to the user.
  
  

Reliability and accuracy

• Zero-party data is explicit but limited in scope, users may state preferences that don’t always translate into real behavior.
  
• First-party data reflects actual user actions, making it highly valuable for behavioral analysis.
  
• Third-party data often lacks transparency, with varying quality and outdated or mismatched audience segments.

Ownership and control

• Zero- and first-party data are under the company’s control, stored in its own systems, and easier to audit.
  
• Third-party data is “rented”, accessing it depends on external providers, who may change terms or discontinue datasets.
  
  

Compliance and transparency

• Zero-party data is the strongest from a compliance perspective because users knowingly provide it.
  
• First-party data is generally acceptable if collected with proper consent (especially when cookies or tracking tech are involved).
  
• Third-party data is the most problematic, often lacking clear consent pathways — a key reason for its regulatory and technical decline.
  
  

Taken together, these differences explain why marketers, analysts, and legal teams must rethink their data strategies. Zero- and first-party data offer sustainability and trust, while third-party data’s future is shrinking both technically and legally.

Implications for different teams

Marketing teams: personalization under constraints

The end of third-party cookies limits the ability to retarget users across the open web or build large-scale lookalike audiences. For marketers, this means shifting from broad reach to deeper relationships.

• Personalization and segmentation now depend on zero- and first-party data. Preference centers, loyalty programs, and email marketing are becoming critical tools. A 2024 Gartner survey found that 71% of marketers planned to increase investments in loyalty programs as a direct response to cookie deprecation (Gartner, 2024).
  
  
• From programmatic to relationship-based marketing: strategies are moving away from anonymous third-party segments toward communities, brand memberships, and owned channels.
  
  
• Email and CRM systems are regaining prominence as sustainable channels, where engagement can be tracked transparently and consent is easier to manage.
  

Analytics and data science teams: working with data gaps

Analytics professionals face the challenge of modeling user behavior with fewer external signals.

• Data quality over quantity: with smaller but richer zero- and first-party datasets, accuracy and completeness matter more than volume. Poor consent handling or fragmented data pipelines can undermine insights.
  
  
• Server-side tracking is gaining traction, allowing companies to own and control the data flow rather than depending on browser-based methods vulnerable to blocking (Forrester, 2023).
  
  
• Customer Data Platforms (CDPs) help unify datasets across touchpoints, giving analysts a single source of truth.
  
  
• Machine learning with constrained datasets: analysts increasingly need to build predictive models that work with smaller, privacy-safe datasets — making the quality of input data decisive.
  
  
• Cross-device and omnichannel attribution becomes harder as third-party signals vanish. New approaches include probabilistic attribution and privacy-preserving methods like data clean rooms.

Legal and compliance teams

Legal departments are tasked with making sure new data strategies meet both regulatory requirements and user expectations.

• Regulatory compliance: GDPR, CCPA, and newer acts (like the EU’s Digital Markets Act) are clear on the need for transparency and explicit consent, particularly around cookies and tracking.
  
  
• Consent frameworks: updates such as IAB’s Transparency and Consent Framework (TCF 2.2, launched 2023) are shaping how consent is captured and communicated to ad tech partners (IAB Europe, 2023).
  
  
• Risk management: reliance on third-party data introduces risks of non-compliance, especially when data brokers cannot prove valid user consent. Enforcement is rising, with fines against Meta, TikTok, and other major platforms highlighting regulators’ focus on tracking practices.
  
  
• Data sovereignty and localization: as more countries introduce local storage requirements, legal teams must guide how and where zero- and first-party data can be processed.

Strategic shifts in data collection

The most immediate change is the continued phase-out of third-party cookies. Google Chrome, still dominant with ~65% global market share (StatCounter, 2025), began disabling them for 1% of users in early 2024 and expanded the rollout in 2025 under its Privacy Sandbox initiative. While these tools aim to preserve advertising functionality without cross-site tracking, adoption and effectiveness remain debated among advertisers and regulators.

Server-side tracking for data control

As browsers restrict client-side tracking, server-side tagging is becoming a key solution in building a resistant setup conquering data gaps. Instead of relying on fragile browser cookies, data is collected via a company’s own server infrastructure, giving businesses greater control over data quality, governance, and compliance. 

Closing data gaps with AI-powered solutions

AI models are being used to extract more value from higher-quality datasets. Machine learning tools can identify intent, cluster users, and optimize campaigns with fewer signals, provided the underlying first- and zero-party data is accurate. McKinsey (2024) reports that companies leading in AI-driven personalization are achieving revenue lifts of 10–20% despite data restrictions. JENTIS customers have achieved up to 25% ROAS uplifts by activating lost conversions with synthetic data.

Consumer trust as a new currency

Finally, consumer expectations are shifting. Transparency and control are no longer “nice to have” but central to brand perception. Cisco’s Consumer Privacy Survey 2024 found that 76% of respondents said they would not buy from a company they don’t trust with their data. This means trust is not just a compliance matter but a competitive advantage.