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The rise and fall of third-party cookies: how the technology that powered digital advertising for 20 years became obsolete due to privacy concerns and regulation.
Simul Sarker
CEO of DataCops
Last Updated
October 25, 2025
You're browsing a website for running shoes. You don't buy anything. An hour later, you're scrolling through social media and suddenly those same shoes appear in an ad. Tomorrow, they follow you to a news site. By next week, they're haunting you across the entire internet.
You've just experienced the third-party cookie ecosystem in action. And if you find this experience creepy, unsettling, or invasive, you're not alone. In fact, you're part of a global movement that finally killed this technology. But the story of how we got here, why third-party cookies were built in the first place, and what went wrong is far more complex than it might seem.
To understand third-party cookies, we need to go back to 1994, when the internet was barely a teenager. Netscape, the dominant browser of the era, faced a critical problem: stateless protocol. HTTP, the language of the web, didn't remember anything between requests. Every time you visited a website, the server had no way to know if you'd been there before.
This sounds like a minor technical issue, but it created massive problems for early e-commerce. Websites couldn't remember what was in your shopping cart. They couldn't recognize returning customers. They were essentially treating every visit as if you were a complete stranger.
Lou Montulli, an engineer at Netscape, borrowed a concept from real-world bakeries. Just as a baker might write notes on a card to remember a regular customer's preferences, Montulli proposed storing small text files on users' computers. When visitors returned, the browser would send these files back to the website automatically. The technology was named after a snack food (the reasoning remains somewhat obscure), and cookies were born.
First-party cookies were revolutionary. They enabled online shopping carts, user logins, and personalization. A website could remember that you preferred dark mode or that you'd already closed their cookie banner. These cookies lived on your computer but were only readable by the website that set them. It was consensual, straightforward, and useful.
For about four years, this was the only type of cookie that existed. And then everything changed.
In 1998, the advertising industry discovered first-party cookies and saw potential. Specifically, they saw potential to track people across the entire internet.
Here's how the scheme worked: Advertising networks would create small image files (often invisible 1-by-1 pixel "tracker pixels") and embed them on thousands of websites. When your browser loaded a webpage, it would also load these tracking pixels from the ad network's servers. Because cookies are automatically sent whenever your browser communicates with a server, the ad network would receive the information stored in its cookies. Each time you visited a new website with the same ad network's pixel, that company would add a new data point to your profile.
Third-party cookies were born not out of technical necessity, but out of economic incentive. Advertisers discovered they could build detailed dossiers of users' browsing behavior without ever asking for permission, and more importantly, without users even knowing it was happening.
This was enormously profitable. Advertising networks could charge a premium for "behavioral targeting" - showing ads based not just on what website you were visiting, but on your entire browsing history across the internet. A user looking at gardening websites could be served ads for fertilizer across every other website they visited, even hours or days later.
For two decades, third-party cookies became the foundational technology of digital advertising. By the early 2000s, companies like DoubleClick, Google (which acquired DoubleClick in 2007), and dozens of other ad networks had built multi-billion-dollar empires on the back of this technology.
The sheer scale of the tracking apparatus was difficult for average internet users to comprehend. A 2012 study by AT&T researcher Jennifer King found that on a typical day, users would encounter an average of 105 distinct tracking cookies. By 2020, that number had reached into the thousands per person, per day.
The value seemed obvious to the advertising industry. David Cohen, senior analyst at Gartner at the time, noted that behavioral data allowed advertisers to "reach customers at the right time with the right message." From a pure advertising effectiveness standpoint, this was demonstrably true. Third-party cookies worked. They improved ad relevance, reduced wasted ad spending, and enabled the free internet that billions of people had come to depend on.
What the industry hadn't fully grappled with was the cost.
The turning point came gradually, then suddenly.
In 2010, the Pew Research Center found that 68% of internet users were concerned about online tracking. By 2019, that number had climbed to 79%. More importantly, concern had shifted from abstract worry to concrete action. Browser vendors began offering "Do Not Track" headers, though advertisers mostly ignored them. Apple introduced Intelligent Tracking Prevention in Safari, a feature that limited third-party cookies' effectiveness on its browser. Mozilla did the same with Firefox.
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But the real catalyst came from an unexpected direction: regulation.
In 2018, Europe enacted the General Data Protection Regulation (GDPR). Unlike previous privacy laws that mostly applied to specific industries, GDPR was broad, ambitious, and came with massive fines. For the first time, companies collecting data about internet users needed explicit consent. Third-party cookies, which operated almost entirely without user knowledge or consent, became legally problematic.
The impact was seismic. Websites across Europe suddenly needed to display cookie banners asking for permission. Most users rejected these requests when given a meaningful choice, forcing advertisers to confront an uncomfortable truth: most people, when asked directly, didn't want to be tracked.
What began in Europe spread quickly. California's CCPA (2020), similar regulations in Canada, and emerging privacy laws in numerous other jurisdictions put third-party cookies on an unsustainable trajectory.
But the most significant blow came from an unexpected source: Google, the company whose ad network had profited most from third-party cookies.
In January 2020, Google announced it would phase out third-party cookies from Chrome, the world's dominant browser. This wasn't a sudden principled stand. Google had been facing increasing regulatory pressure and public scrutiny. More pragmatically, Google had begun developing new technologies that would let the company continue tracking and targeting ads without relying on third-party cookies, essentially cutting out smaller ad networks and advertisers who lacked Google's technological infrastructure.
The announcement set off a scramble across the advertising industry. If Chrome, which controlled roughly 65% of browser market share, was eliminating third-party cookies, the entire digital advertising ecosystem would need to be rebuilt.
"This move by Google is both a genuine privacy improvement and a competitive advantage," explains Rishad Tobaccowala, former chief strategist at Publicis Groupe. "It removes a privacy vulnerability that Google had long benefited from, while simultaneously making it harder for smaller competitors to engage in the same targeting practices. That's the paradox of this moment."
As the deadline for third-party cookie elimination approached (initially planned for 2022, repeatedly delayed, finally scheduled to begin in early 2025), the industry scrambled to develop replacements.
Google proposed the Privacy Sandbox initiative, which included various technologies like Federated Learning of Cohorts (FLoC) and Topics API. The idea was to move targeting from individual-level tracking to cohort-based targeting - grouping users by interests without exposing their full browsing history. Privacy advocates and competitors both heavily criticized these proposals, arguing they simply repackaged surveillance in different language.
Other proposals included Universal IDs (persistent identifiers created through email addresses or phone numbers), contextual targeting (showing ads based on current page content rather than browsing history), and first-party data strategies (where websites collect their own data and advertisers buy access to those audiences directly).
None of these alternatives achieved the elegance and simplicity of third-party cookies. Each required buy-in from multiple parties. Each had limitations. And crucially, none matched the sheer effectiveness of the behavioral data third-party cookies had enabled.
Meanwhile, other browsers simply eliminated third-party cookies entirely. Safari has blocked them since 2017. Firefox followed suit in 2019. By late 2024, the percentage of internet users still fully exposed to third-party cookie tracking had plummeted.
Understanding why third-party cookies failed requires looking beyond technology. They failed because of a fundamental mismatch between the value they provided and the cost they imposed.
The value was real but narrow. Third-party cookies worked beautifully if you were an advertising company trying to maximize ad relevance and campaign effectiveness. But for everyone else, the value proposition was much murkier. Regular internet users saw no benefit to being tracked across thousands of websites. Website publishers often didn't benefit directly; they were mostly helping ad networks. Only the ad tech intermediaries saw clear returns.
The cost was broad and persistent. Users experienced the creepiness of behavioral tracking. They saw their browsing histories reflected in ads following them around the internet. They lost control over their own data. Privacy advocates warned about the societal implications of detailed behavioral surveillance. Regulators responded. And once people understood what was happening, widespread opposition became inevitable.
Third-party cookies also became a victim of their own success. By enabling such detailed tracking, they eventually triggered the regulatory backlash that killed them. Had the tracking been less invasive or more transparent, it might have survived longer. But the effectiveness that made them valuable also made them untenable in a world increasingly concerned with privacy.
There's also a technical reality that often gets overlooked. The internet had evolved. Modern browsers had become sophisticated enough to implement privacy protections that third-party cookies couldn't survive. Once browser vendors decided third-party cookies needed to die, there was no technological solution that would save them. The cookies existed only because browsers chose to allow them.
As third-party cookies have been phased out, some predictions have proven true and others surprisingly false.
The digital advertising industry didn't collapse, contrary to some doomsayers. CPMs (cost per thousand impressions) initially dipped, but stabilized. Large publishers with direct audience relationships and first-party data actually strengthened their positions. Google and Meta continued to profit enormously because they own the platforms where users engage and create first-party data naturally.
What actually changed was the redistribution of power. The cookie-based ecosystem that allowed thousands of smaller ad networks and data brokers to operate has largely consolidated. The network effects favor large platforms that directly interact with users. Smaller advertisers and ad tech companies have found it much harder to operate at scale. This consolidation may ultimately prove bad for competition, even as the elimination of third-party cookies was marketed as a privacy victory.
Advertisers did adapt. They've returned to older tactics like contextual advertising (showing ads based on the current page content rather than user history). They've invested heavily in first-party data collection. They've built email lists and loyalty programs. They've abandoned some campaigns as too difficult to execute without behavioral tracking.
For users, the immediate impact has been mixed. Some saw targeted ads decrease noticeably. Others saw little change, because they existed in ecosystems (Google, Meta, Amazon) where first-party data provides all the targeting needed. Privacy hasn't necessarily increased dramatically; it's just shifted from a broadly distributed tracking system to even more centralized surveillance by platform owners.
The death of third-party cookies wasn't primarily a technical failure. It was a values failure. The technology worked. It was profitable. It achieved what it was designed to do. But it did so in ways that increasingly conflicted with how people wanted to be treated.
Third-party cookies ultimately failed because society decided that the bargain they represented was unfair. Users hadn't consented to being tracked. Website publishers didn't fully understand what was happening on their sites. Regulators increasingly viewed the behavior as unacceptable. And once that consensus formed, no amount of technical innovation or minor modifications could save the system.
The lesson for the future of technology is important. Tools can be powerful and profitable and still fail if they lack legitimacy. Privacy isn't just a regulatory requirement or a technical feature - it's increasingly a fundamental value that shapes what technologies survive and which ones disappear.
As we move further into the post-cookie era, new questions emerge. Will the alternatives prove sustainable? Will regulations become more stringent? Will new technologies emerge that rebalance privacy and personalization in ways that feel fairer to users?
The answers remain uncertain. But one thing is clear: the era of invisible, unopinionated, system-wide tracking by default is over. What replaces it will be determined not just by technologists and advertisers, but by users, regulators, and society's collective decisions about what kind of internet we want to live in.
The cookie didn't fail because it wasn't clever enough. It failed because it was eventually judged and found wanting by the people it was tracking.
