What Are Cookies? Types, Uses & Privacy Explained

If you have ever visited a website, you have encountered cookies. These small text files are a fundamental part of how the internet works – powering everything from login sessions to personalized advertising. But what is a cookie on a website, exactly? And why have cookies become one of the most discussed topics in online privacy?

In this guide, we explain what cookies are, how they work, the different types you need to know about, and what the shift away from third-party cookies means for publishers in 2026.

What Is a Cookie?

A cookie is a small piece of data that a website stores on your browser when you visit it. Cookies are plain text files – they cannot run code or carry viruses. They typically contain a name-value pair, the domain that set the cookie, and an expiration date.

When you return to that website, your browser sends the cookie back to the server. This is how websites “remember” you – whether that means keeping you logged in, remembering items in your shopping cart, or recalling your language preference.

Cookies were invented in 1994 by Lou Montulli, an engineer at Netscape, to solve a practical problem: HTTP is a stateless protocol, meaning each request between browser and server is independent. Without cookies, websites would have no way to remember anything about you between page loads.

How Do Cookies Work?

The process is straightforward:

1. You visit a website. The server sends an HTTP response that includes a Set-Cookie header with the cookie data.
2. Your browser stores the cookie. It saves the text file locally on your device.
3. You return to the site. Your browser automatically attaches the cookie to the request via the Cookie header.
4. The server reads the cookie. It uses the data to personalize your experience – loading your preferences, maintaining your session, or identifying you for analytics.

Cookies can only be read by the domain that set them (with some exceptions for third-party cookies, which we cover below). They have size limits – typically 4KB per cookie – and browsers limit the total number of cookies per domain.

Types of Cookies

Not all cookies are the same. They can be classified by their lifespan and by who sets them.

By Lifespan: Session Cookies vs Persistent Cookies

Session cookies are temporary. They exist only while your browser is open and are deleted automatically when you close it. What is a session cookie used for? Typical uses include maintaining your login state as you navigate between pages, keeping items in a shopping cart during a single visit, and storing temporary form data.

Persistent cookies remain on your device for a set period – anywhere from a few days to several years – or until you manually delete them. They are used for remembering login credentials (the “remember me” checkbox), storing language and display preferences, and tracking user behavior across multiple visits for analytics.

By Origin: First-Party vs Third-Party Cookies

This is where privacy gets involved.

First-party cookies are set by the website you are visiting directly. If you go to example.com, any cookies set by example.com are first-party cookies. They are generally considered essential for website functionality and are widely accepted by both browsers and privacy regulations.

Third-party cookies are set by a domain other than the one you are visiting. For example, if example.com loads an ad from adnetwork.com, the ad network can set a cookie on your browser under the adnetwork.com domain. Because the same ad network serves ads on thousands of websites, it can use that cookie to track your browsing activity across all of those sites – building a profile of your interests, demographics, and behavior.

This cross-site tracking capability is why third-party cookies have become the central focus of privacy debates and regulation.

Other Cookie Types

You may also encounter these terms:

• Strictly necessary cookies – Required for the website to function (e.g., authentication, security). These are typically exempt from consent requirements.
• Performance/analytics cookies – Collect anonymous data about how visitors use a site (page views, bounce rates, load times).
• Functionality cookies – Remember user preferences like language, region, or display settings.
• Targeting/advertising cookies – Track users across sites to deliver personalized ads. Almost always third-party.

What Are Cookies Used For?

Cookies serve many purposes on the modern web. Here are the main ones:

Authentication and Sessions

When you log in to a website, a session cookie stores a unique identifier so the server knows you are authenticated. Without this cookie, you would need to enter your password on every single page.

Personalization

Persistent cookies let websites remember your preferences – dark mode settings, currency selection, language choice, or whether you have dismissed a notification banner.

Analytics

Tools like Google Analytics use cookies to distinguish unique visitors, track pageviews, and measure how users interact with a site. This data helps publishers understand what content performs well and where visitors drop off.

Advertising

This is the most controversial use. Third-party cookies enable programmatic advertising – the automated buying and selling of ad impressions in real time. Advertisers use cookies to build audience profiles, measure click-through rates, retarget users who visited their site, and attribute conversions (someone who saw an ad and later made a purchase).

For publishers, these advertising cookies are directly tied to CPM rates and revenue. Personalized ads – served using cookie data – generally generate higher RPM than non-personalized alternatives.

Third-Party Cookies and Privacy

What are third-party cookies, and why are they so controversial? The issue is not the cookie itself – it is the tracking capability they enable.

When ad networks, social media platforms, and data brokers use third-party cookies to follow users across the web, they can build detailed behavioral profiles without users fully understanding what is being collected. This has raised significant privacy concerns:

• Lack of transparency – Most users do not know which companies are tracking them or what data is collected.
• No meaningful consent – Historically, cookies were set without asking users for permission.
• Data aggregation – Individual cookies seem harmless, but when aggregated across sites, they paint a comprehensive picture of someone’s interests, habits, and identity.

The End of Third-Party Cookies

The major browsers have been phasing out third-party cookie support:

• Safari fully blocked all third-party cookies by default in March 2020 with Safari 13.1 – the culmination of Apple’s Intelligent Tracking Prevention (ITP) program, which had progressively restricted them since 2017.
• Firefox rolled out Enhanced Tracking Protection, blocking known trackers by default.
• Google Chrome – the last major holdout – initially planned to deprecate third-party cookies but reversed course in July 2024. Rather than removing them, Chrome maintains its existing privacy settings, allowing users to manage cookie preferences through the browser’s Privacy and Security settings.

Even with Chrome keeping third-party cookies as an option, the overall trend is clear: the industry is moving toward cookieless monetization strategies and consent-based models.

Cookie Regulations: GDPR, CCPA, and ePrivacy

Privacy regulations have fundamentally changed how websites use cookies. Here are the key laws publishers need to know:

GDPR (General Data Protection Regulation)

The EU’s GDPR requires websites to obtain explicit, informed consent before setting non-essential cookies for users in the European Economic Area and UK. Switzerland requires consent for advertising and profiling cookies under its Federal Act on Data Protection (FADP), though its overall approach differs from the GDPR in some respects. In practice, Google’s EU User Consent Policy requires publishers using Google ad products to obtain consent from users in all three regions. This means:

• Users must actively opt in to cookies (no pre-ticked boxes).
• The consent request must clearly explain what cookies are used and why.
• Users must be able to withdraw consent as easily as they gave it.
• Only strictly necessary cookies can be set without consent.

GDPR violations can result in fines of up to 4% of global annual revenue or 20 million euros, whichever is greater.

ePrivacy Directive (Cookie Law)

Sometimes called the “Cookie Law,” the ePrivacy Directive specifically addresses electronic communications and cookie use in the EU. While the GDPR covers personal data broadly, the ePrivacy Directive specifically requires consent for storing or accessing information on a user’s device – which includes cookies. The two regulations work together, with the ePrivacy Directive providing cookie-specific rules within the GDPR’s broader framework.

CCPA / CPRA (California Consumer Privacy Act)

The CCPA takes a different approach. Instead of requiring opt-in consent, it gives California residents the right to opt out of the “sale” or “sharing” of their personal information – which includes data collected via third-party cookies for targeted advertising. Publishers must provide a clear “Do Not Sell or Share My Personal Information” link, honor opt-out requests (including Global Privacy Control signals), and disclose their data collection practices.

US State Privacy Laws

20 US states have now passed comprehensive privacy laws, many with cookie-related requirements. These laws generally follow the CCPA’s opt-out model rather than the GDPR’s opt-in approach, but each has unique provisions publishers need to be aware of.

What Publishers Need to Know About Cookies

For website publishers, cookies sit at the intersection of revenue and compliance. Here is what matters most:

Consent Management Is Not Optional

If your site has visitors from Europe, the US, Brazil, or any of the many other countries that have adopted privacy regulations, you need a way to collect and manage cookie consent. This is not just about avoiding fines – ad networks like Google require publishers to have a certified Consent Management Platform (CMP) to serve personalized ads in regulated regions.

Industry frameworks help standardize how consent is communicated across the ad tech supply chain. In Europe and Canada, the IAB Transparency and Consent Framework (TCF) provides this standard. In the US, the IAB’s Global Privacy Platform (GPP) serves a similar role, transmitting user opt-out preferences to advertisers and vendors.

Cookie Consent Affects Ad Revenue

When users decline cookie consent, publishers can only serve non-personalized ads – which typically earn significantly lower CPMs. Consent rates directly impact the bottom line. This is why cookie banner design, wording, and placement matter: a well-designed consent interface that clearly explains the value exchange can achieve higher opt-in rates while remaining fully compliant.

How Clickio Helps Publishers Manage Cookie Consent

Clickio Consent is a Google-certified Consent Management Platform that simplifies cookie compliance for publishers. It handles the complexity of global privacy regulations so you can focus on content and revenue.

• Multi-regulation compliance – Covers GDPR, US state privacy laws, LGPD, and other global regulations from a single platform.
• Google Consent Mode v2 – Automatically adjusts Google tag behavior based on user consent, ensuring proper signal communication to Google Analytics, Ads, and Ad Manager.
• GPC signal support – Recognizes and honors Global Privacy Control opt-out signals from user browsers.
• Customizable cookie banners – Custom colors and branding, flexible close-button layouts, custom consent text, and support for 26+ languages (multi-language on Pro+ and above).
• Revenue protection – Consent reporting and analytics help you understand opt-in rates and their impact on ad revenue. A/B testing lets you optimize your consent interface for higher acceptance.
• Quick implementation – Deploy on web in minutes, with AMP support on Pro and mobile app SDKs (Android, iOS, Flutter, React Native) on Pro+ and above.

Clickio Consent offers a free plan to get started, with paid tiers for additional features like US privacy law support, vendor management, A/B testing, and mobile app SDKs.

Frequently Asked Questions

Are cookies dangerous?

No. Cookies are plain text files – they cannot execute code, install malware, or access other files on your device. The privacy concern is not about cookies themselves, but about how the data they collect can be used to track browsing behavior across websites.

What happens if I delete all my cookies?

You will be logged out of all websites, and any saved preferences (language, display settings, shopping carts) will be reset. Websites will treat you as a new visitor on your next visit.

What is the difference between cookies and local storage?

Both store data in the browser, but they work differently. Cookies are sent to the server with every HTTP request and have a 4KB size limit. Local storage (part of the Web Storage API) stays in the browser, is not sent to the server automatically, and can store up to 5-10MB. Local storage is not subject to the same automatic transmission behavior, but privacy regulations like the GDPR cover both technologies.

Do all websites use cookies?

Nearly all websites use at least some cookies. Even simple static sites often use analytics cookies. Any site with login functionality, e-commerce features, or advertising will use multiple types of cookies.

Conclusion

Cookies are a foundational technology of the web. They make login sessions, personalization, analytics, and digital advertising possible. But the way cookies are used – particularly third-party cookies for cross-site tracking – has driven a wave of privacy regulations and browser restrictions that every publisher needs to navigate.

The key takeaway: first-party cookies remain essential and are not going away. Third-party cookies are declining in importance. And regardless of which cookies you use, transparent consent management is now a legal requirement in most markets.

For publishers looking for a simple way to handle cookie consent across all major privacy regulations, Clickio Consent offers a free, Google-certified solution that takes minutes to set up.