I know that Google is collecting much information with Analytics. Analytics uses first-party cookies, so Google shouldn't be able to recognize a person on different websites. How is the Cross-Domain-Tracking working?

Let's say a person visits website A with GA and Google tracks it an stores the information on a server (Website sets first-party-cookie)
Now the person visits website B with GA and Google tracks it again (Website B can't read the first-party-cookie of website A, Website B sets another first-party-cookie)

Now the person visits website C with AdSense. How does Google know which advertisment they should show? Without third-party-cookies they can't know that the visitor was on the websites A and B before.

  • You are asking way to many questions at the same time here. Try narrowing down the scope.
    – dasickle
    Commented Dec 15, 2015 at 13:14
  • I just want to know, how Google Analytics can perform Cross-Domain-Tracking with first-party cookies and how Google Analytics and Google AdSense work together.
    – maxeh
    Commented Dec 15, 2015 at 13:18
  • I made some changes, now the question should be clear.
    – maxeh
    Commented Dec 15, 2015 at 14:04
  • Have you tried googling your question about cross domain tracking?
    – nyuen
    Commented Dec 15, 2015 at 15:07
  • I found several explanations how a user can be tracked, for example with browser fingerprinting. But the configuration of a browser isn't always unique. Moreover the IP-adress could be used to identify a user, but the IP changes daily and many websites only send anonymized IP-adresses (without last 8 Bit) to Google. Maybe Google uses a combination of fingerprinting and the shortened IP to identify a user, but that would only work, if the IP stays the same. Otherwise Google wouldn't be able to recognize the user a day later; this would be possible with third-party-cookies, which they not use
    – maxeh
    Commented Dec 15, 2015 at 15:31

2 Answers 2


You use the same snippet (and therefore the same cookies) on each domain.

You then tell GA, through configuration, that both/all domains are acceptable and that data (cookies) should be shared.

Before setting up cross-domain tracking I thought it was linking different GA properties (UA-XXXX-1 and UA-XXXX-2) on different domains and that is not the case, it is the same GA property (UA-XXXX-1) used on different domains.

Sorry but that's as detailed as my understanding is...hope it helps.

And no, it doesn't involve browser fingerprinting (which is actually quite reliable...above 80% from what I understand) GPU fingerprinting, IP address tracking etc.

Don't get me wrong, it wouldn't surprise me if Google used every technology they could get to track users, they just don't make that available through GA. Without User ID, GA is cookie based and while it can include 3rd party cookies (demographic reporting), somehow they make it work cross-domain with 1st party cookies..if configured correctly.

  • I was thinking from Googles point of view. How can they recognize the user in order to show the right advertisement? I added an example in my question, maybe you know the answer.
    – maxeh
    Commented Dec 17, 2015 at 11:16
  • I understand better now but it doesn't help because GA can use some 3rd party cookies (DoubleClick) if you enable demographic reporting. Traditional remarketing snippets from AdWords use JS (cookies) but also have a tracking pixel fallback. And you can now use the GA itself (without a separate AdWords remarketing snippet) to do remarketing...there's just way too many things to be able to explain how they all might work.
    – adam-asdf
    Commented Dec 18, 2015 at 17:22

Google does not use Google Analytics for the purpose of choosing which ads to show.

Google AdSense ads set their own third party cookies. Google tracks users across multiple domains with cookies set by ads, not with cookies set by Google Analytics.

  • Ok this makes sense, but why is Google offering such a big tool for free? What are the advantages for them? Do they want the users to use AdSense and offer Analytics as a "bonus"?
    – maxeh
    Commented Jan 16, 2016 at 15:28
  • Google has said that they won't use data from Google Analytics for any other purpose. There is a lot of speculation about the truth of that statement and what other motives they might have. Entire articles have been devoted to it such as this one: brianclifton.com/blog/2007/07/23/… Commented Jan 16, 2016 at 15:30

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