Get Your Free Guide to Understanding Third-Party Cookies

What Third-Party Cookies Are and How They Work

Third-party cookies are small text files that websites place on your computer or phone to track your activity across different websites. Unlike first-party cookies, which come directly from the website you're visiting, third-party cookies are created by other companies—often advertising networks, analytics firms, or data brokers—that operate across many different sites.

When you visit a website, that site may contain invisible tracking pixels, advertisements, or analytics tools from other companies. These third-party vendors place cookies on your device to monitor which pages you visit, how long you stay, what you click on, and what products you view. This information builds a profile of your browsing habits, preferences, and interests over time.

For example, if you visit an online shoe store and look at running shoes, a third-party cookie from an advertising network might track this activity. Later, when you visit a news website or social media platform, that same advertising network recognizes you and shows you ads for running shoes based on what you viewed earlier. This is called behavioral tracking or retargeting.

According to research from the Mozilla Foundation, the average person encounters tracking from dozens of third-party companies while browsing the web. A 2023 study found that popular websites contained an average of 22 different tracking cookies from third parties. These cookies persist across websites and can track users for months or even years.

Third-party cookies work because advertising networks and data companies have agreements with thousands of websites to place their tracking code on those sites. This creates a vast web of connected tracking across the internet. When you visit any participating website, the network recognizes you through the cookie and adds new information to your profile.

Practical Takeaway: Understanding that third-party cookies track your behavior across many websites helps you make informed decisions about your online privacy. Recognizing how widespread this tracking is enables you to evaluate what personal information you're comfortable sharing and what steps you might take to limit tracking.

The Difference Between First-Party and Third-Party Cookies

First-party cookies and third-party cookies serve different purposes and come from different sources. A first-party cookie is created and managed by the website you're directly visiting. When you log into your email account, for example, a first-party cookie remembers your login information so you don't have to enter your password every time you refresh the page. Similarly, when you add items to an online shopping cart, a first-party cookie stores that information.

First-party cookies are generally considered less invasive because they only track your activity on that specific website. A first-party cookie from an online retailer knows you browsed their site and what products you looked at, but it doesn't track you on other websites. Most websites use first-party cookies to improve your experience—remembering your preferences, keeping you logged in, and storing items in your cart.

Third-party cookies, by contrast, come from companies other than the website you're visiting. These are typically advertising networks, analytics companies, or data brokers. A single third-party cookie can track you across dozens, hundreds, or even thousands of different websites. This creates a much more complete picture of your browsing habits, interests, and behavior patterns.

The practical difference is significant. First-party cookies help websites provide services you've requested. Third-party cookies help advertisers and data companies build detailed profiles about you that they can sell or use to target you with advertisements. A 2022 study by the Pew Research Center found that 72% of adults in the United States believe companies track their online behavior, and 81% said they don't feel in control of what information about them is collected.

First-party cookies are necessary for many websites to function properly. Third-party cookies are optional from the perspective of website functionality—websites could operate fine without them. However, many websites include third-party tracking because advertising networks pay them for the privilege of tracking visitors. This revenue model has made third-party cookies extremely common on the web.

Practical Takeaway: Recognizing the difference between first-party and third-party cookies helps you understand which tracking is necessary for websites to work properly and which tracking is primarily for advertisers' benefit. This knowledge allows you to make more informed choices about browser settings and privacy tools.

How Third-Party Cookies Collect and Use Your Data

Third-party cookies collect specific types of information about your online behavior. They track which websites you visit, how much time you spend on each page, which links you click, what products you view, and whether you make purchases. They also collect information about your device, your approximate location based on your internet address, and the time of day you're browsing.

This collection happens largely without your direct awareness. The cookies work in the background whenever you visit a website that contains third-party tracking code. Over time, these small pieces of information accumulate to create a detailed profile of your interests, habits, and preferences. A person who frequently visits technology blogs, reads about fitness, and shops for outdoor equipment will have a different profile than someone who visits cooking websites and reads about gardening.

Once collected, this data is used in several ways. Advertisers use it to show you targeted advertisements. If your profile indicates you're interested in travel, you'll see more travel ads. If you've looked at laptops but haven't bought one yet, you'll see laptop advertisements across multiple websites. This is called behavioral targeting, and it's extremely common in online advertising.

Data brokers purchase this information from advertising networks and compile it into even larger profiles that they sell to other companies. Some data brokers create thousands of data points about individual people and sell this information to insurance companies, employers, lenders, and other businesses. According to a 2023 Federal Trade Commission report, the data broker industry processes personal information about billions of people, often without those people's knowledge.

Third-party cookies also enable what's called cross-device tracking. Companies can connect your browsing on your phone with your browsing on your computer by using email addresses, usernames, or device fingerprints. This means your profile may follow you across multiple devices, creating an even more comprehensive picture of your online activity.

Practical Takeaway: Understanding how your data is collected and used across websites helps you recognize why you see certain advertisements and why companies seem to know so much about you. This awareness is the first step in deciding what privacy measures might be right for your situation.

Privacy Concerns and Risks Associated with Third-Party Tracking

Third-party cookie tracking raises several privacy concerns that affect millions of internet users. One major concern is that people often don't know they're being tracked or understand the extent of the tracking. Most websites have privacy policies that mention tracking cookies, but these policies are written in legal language that many people find difficult to understand. A study by Carnegie Mellon University found that if a person read every privacy policy on websites they visited, it would take approximately 244 hours per year.

Data collected through third-party cookies can be used in ways you might not expect or approve of. For example, health insurance companies might use browsing data to identify people researching expensive medical conditions. Employers might use such data to screen potential job applicants. Lenders might use it to determine credit terms. A person who searches for information about mental health conditions, addiction recovery, or medical treatments could have that information used against them by insurers, employers, or lenders.

Data breaches pose another significant risk. When data brokers and advertising networks accumulate information about millions of people, they become targets for hackers. When these systems are breached, personal information is exposed. The Identity Theft Resource Center reported over 1,800 data breaches in 2023 alone, exposing more than 354 million personal records. Much of this data comes from companies that collected information through tracking cookies.

Third-party cookie tracking also creates security vulnerabilities. Criminals can buy detailed profiles from data brokers or intercept tracking cookies to identify vulnerable targets for scams. Someone researching expensive treatments might be targeted by medical scams. Someone looking at luxury items might be targeted for fraud. The profiles created through tracking cookies essentially create a target list for criminals based on interests and vulnerabilities.

There are also concerns about discriminatory targeting and manipulation. Advertisers can target certain groups with different ads or prices. Studies have shown that some companies display different prices or products to different demographic groups based on data collected through tracking. Political campaigns and misinformation networks use tracking data to microtarget people with tailored messages designed to influence their behavior.

Practical Takeaway: Being aware of these risks helps you