Ad Serving Technology – the distinction between first and third party cookies?

First party vs. third Party Cookies


There are two main types of cookie. The “first party cookie” is placed on the user’s computer or ‘dropped’ by the website the user is visiting. By dropping, we mean that a remote machine or server sends a tiny file to user’s computer or device, whereby the file is delivered and remains until it is deleted or removed. This file is a cookie and usually contains the cookieID, the timestamp of when the cookie was dropped and the filename for the file will reference the domain it came from. If a website drops a cookie file onto your computer from its own domain, it is a first party cookie (The web address of the website is part of the websites “domain” so in “” is the domain and “autos.” is the subdomain). If a website drops a cookie on your machine from another domain (such as the domain belonging to a third party ad server) this is called a “third party cookie”.

Cookies are a website’s way of remembering some information about you as a user because once they have been dropped they remain on the machine until they are removed.  Since the cookie is residing on the user’s machine it is said to ‘live’ on the “client side” and the cookie remains as a signpost or unique reference point, for a website to lookup that unique number against its own database (where there may be more information about each cookie stored on the databases our its own machines; this is called the “server side”)

This lookup or matching process allows a website to ‘remember’ things like some settings or changes the user may have made to a website. Most commonly the first party cookie can be used to remember the information the user put into forms on a website, (so that when they visit that site again, they save time by not having to re-input this information). This is very useful when you, as a user, have to login to a website each time and it remembers your username for instance.

Third party cookies such as those belonging to the third party ad server have a record of the user’s activity matched alongside engagement with an ad campaign. The ad server can report on whether the user saw an ad, clicked on an ad, or went on to buy a product after seeing or clicking an ad online. To be clear, it is not the actual user’s name that the server is remembering, but the unique reference number stored in that user’s cookie. The server stores no personally identifiable information and so never knows that you are you; it just knows that your cookie allows the server to remember behavioral information about that cookieID. Those readers who live and breathe Excel and databases can begin to picture a master table sitting in the deep backend of the ad server, where every ad engagement can be tied back to a cookieID..

To find out more about using unique cookies in advertising technology across all digital channels, get a copy of: Ad Serving Technology – Understand the Marketing revelation that commercialized the Internet – available now from..

….Amazon UK:

Or Amazon USA:

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