We'd love to hear from you!
See More

If you have any questions about our services, need some help, or just want to chat, we're here for you. Simply fill out the form below, and one of our team members will reach out to you soon.

If you have questions regarding U.S. consumer data privacy, click here.

Contact Epsilon
P.O. Box 1478
Broomfield, CO 80038
Attn: Privacy
(866) 267-3861
[email protected]

Privacy Policy

Your Privacy Choices

Select...
Select Country

I agree to receiving marketing communications from Epsilon and its affiliates, and agree to the processing of my personal data in accordance with and as described in the Privacy Policy. You may withdraw your consent at any time. For more details see our Privacy Policy or update your Preferences.

What is the difference between first- and third-party cookies? Estimated reading time: 5 minutes
Blog

What is the difference between first- and third-party cookies?

By: Epsilon Marketing | December 8, 2025

Cookies identify online users and have become a mainstay of digital advertising. As web servers have no memory of their own, cookies are used to make websites remember a user’s action, so they aren’t asked to perform a task again and again. As a result, they help provide a better, more personalized user experience.

And while most marketers know this broad definition, getting into the weeds regarding the different types of cookies and how they differ from one another can be trickier. However, with the current trend of third-party cookie deprecation, it’s more important than ever for marketers to gain a nuanced understanding.

So, what are third-party cookies? And how are they different from the other types of cookies, namely first-party cookies? Read on to find out.

Types of cookies

Let’s run through definitions of first- and third-party cookies before taking a look at how they differ from one another.

What are first-party cookies?

What are first-party cookies? First-party cookies are created and stored by the website you are visiting directly. They are used to collect user data for analytics, remember language settings, and store login information.

What are third-party cookies?

As the name implies, third-party cookies are created and placed by third parties other than the website you are visiting directly. Some common uses include:

  • Cross-site tracking: the practice of collecting browsing data from numerous sources (websites) that details your activity
  • Retargeting: using search activity to retarget visitors with visual or text ads based on the products and services for which they’ve shown interest
  • Ad-serving: making decisions regarding the ads that appear on a website, deciding when to serve these ads, and collecting data (and reporting said data including impressions and clicks) in an effort to educate advertisers on consumer insights and ad performance.

The key differences between third-party cookies and first-party cookies

From the technical perspective, first- and third-party cookies are the same kind of files. The only difference lies in how they are created and used by websites.

First-party cookies are generated by the host domain. They are usually considered good because they help provide a better user experience. These cookies enable the browser to remember important user info, such as what items you add to shopping carts, your username and passwords, and language preferences.

On the other hand, third-party cookies are mostly used for tracking and online advertising purposes.

Here’s a table summarizing the key differences between first- and third-party cookies:

First-Party vs. Third-Party Cookies

The third-party cookie phase-out

Today, users are demanding greater privacy, which includes transparency, choice and control over how their data is used. This means that marketers will have to pivot their advertising strategies since the availability and accessibility of cookies will continue to evolve.

Here’s how the third-party cookie phase-out is expected to affect marketers:

Third-party cookies are crumbling: Now what?

Epsilon's research on this industry shift shows that despite the impact and significance, fewer than half of marketers (46%) feel "very prepared" to market without third-party cookies entirely. Although third-party cookies are still being used in marketing, their availability has greatly decreased in recent years. For example, third-party cookies are not used at all on Apple devices, so any activity on Safari on an iPhone or iPad can not be recognized for ad-serving with those cookies.

If your marketing strategies rely on third-party cookies, it’s time to start exploring alternatives. Look to partners who can provide a stable and scalable ID graph with limited reliance on third-party cookies. Explore tools that can better help you leverage first-party and transactional data. And if you have limited or no first-party data, seek out vendors and partners that do have access to consented first-party data to identify and reach customers across the web. Because publishers have a direct relationship to the visitors to their sites and apps, it’s important to work with them—or vendors who do—to continue personalizing messages with the help of their first-party data.

Still not sure how to pivot your advertising strategies during the third-party cookies phase-out?

How Epsilon can help

Because Epsilon identity resolution capabilities, also known as our COREid, is anchored in deterministic purchase data from individuals, it has limited dependence on third-party cookies. The integrity of this purchase data allows us to have 96% accuracy and industry-leading match and reach rates. As a result, we are able to identify and serve 98% of our ads to individuals, not orphaned cookies or device IDs.

Epsilon’s direct relationships with over 5000 publishers also help us continue to reach consumers without using third-party cookies, because through these relationships we are still able to:

  • Identify consumers from publisher audiences. Publishers generate IDs based on their first-party data, which is then synced with Epsilon’s COREid.​
  • Connect clients’ advertising goals with publishers’ ad inventory​. Our first-party solution in partnership with our publishers helps us better understand the behaviors of users as they interact with publisher sites.
  • Deliver personalized, relevant ads.​ Connecting our COREid with publishers’ IDs improves identification of publisher audiences and match rates.
  • Reach real individuals. Connecting with the publishers’ authenticated user data (logins, registrations) ensures we are serving ads and optimizing based on individuals, not cookies or device IDs, which may overlap.​​

Our years of preparation building people-based identity with first-party strategies and relationships will enable us to continue delivering results for our advertisers, while still providing performance transparency.

Cookies are pieces of data, and future-proofing your marketing strategy always comes back to your data strategy. If you want to build a data strategy that works for today and into the years to come, download our whitepaper for strategic recommendations on how to get your data in order for the marketing of tomorrow.

This article was published on September 22, 2023, and has since been updated.

Digital MediaData
Insights

Related Posts

A man reviews documents at a table with a laptop, while an orange line graphs upward towards a magnifying glass icon with a gear and sparkles, symbolizing optimization. An orange 'E' logo is in the bottom right.
Blog
AI-powered data clean rooms are the next big strategic advantage in marketing
Learn more
Cover for a guide titled "Driving performance with actionable data," showing a man smiling at a laptop with data analysis icons.
Guide
Website personalization guide: Driving performance with actionable data
Learn more
Two smiling men in circular black and white portraits against an orange background with faint line-art icons.
Webinar
Measurement strategies for the ROI-obsessed marketer
Learn more
Explore more insights
Epsilon Logo
  • Platform
    • PeopleCloud
    Capabilities
    • Identity
    • Artificial Intelligence
    • Intelligent Creative
    Products
    • All Products
    • Customer
    • Clean Room
    • Data
    • Services
    • Messaging
    • Loyalty
    • Digital
    • Retail Media
    • Website
    • Publishers
  • By Use Case
    • 1 View: Understand each consumer
    • 1 Vision: Stay relevant over time
    • 1 Voice: Message across channels
    By Industry
    • All Industries
    • Auto
    • Consumer Packaged Goods
    • Financial Services
    • Health
    • Restaurants
    • Retail
    • Travel
    • Tourism
    • Nonprofits
    • Telecom, Media & Entertainment
    • All Resources
    • Research & Insights
    • Case Studies
    • Blog
    • News
    • About Us
    • Culture
    • Partners
    • Pressroom
  • Careers
  • AdChoicesAdChoices Logo
  • Platform

    • PeopleCloud
  • Products

    • All Products
    • Customer
    • Clean Room
    • Data
    • Services
    • Messaging
    • Loyalty
    • Digital
    • Retail Media
    • Website
  • Industries

    • All Industries
    • Auto
    • Consumer Packaged Goods
    • Financial Services
    • Health
    • Restaurants
    • Retail
    • Travel
    • Tourism
    • Nonprofits
    • Telecom, Media & Entertainment
  • Use cases

    • 1 View: Understand each consumer
    • 1 Vision: Stay relevant over time
    • 1 Voice: Message across channels
  • Resources

    • All resources
    • Research & Insights
    • Case Studies
    • Blog
    • News
  • About

    • About Us
    • Culture
    • Partners
    • Pressroom
    • Locations
    • Careers
Consumer Info 
Privacy Policy 
Terms & Conditions 
AdChoices 
Your Privacy Choices 
Privacy Settings 
©2025 Epsilon Data Management, LLC. All rights reserved. All names and logos are trademarks or registered trademarks of their respective owners.