What are cookies?
Cookies are tiny text files that are stored on a user's browser. Most cookies contain a unique identifier called a cookie ID: a string of characters that websites and servers associate with the browser on which the cookie is stored. This allows websites and servers to distinguish the browser from other browsers that store different cookies, and to recognise each browser by its unique cookie ID.
Cookies are widely used by websites and servers to provide many of the basic services that we find online. If you shop on a website, a cookie allows the website to remember which items you've added to your virtual shopping basket. If you set preferences on a website, a cookie allows the website to remember your preferences the next time that you visit. Or, if you sign in to a website, the website might use a cookie to recognise your browser later on, so that you don't have to sign in again. Cookies also allow websites to collect data about user activity, such as how many unique visitors a page receives per month. All these applications depend on the information stored in cookies.
Cookies themselves contain no personally identifiable information. Depending on the publisher’s and the user’s settings, information associated with cookies used in advertising may be added to the user’s Google Account.
Opting out of ads personalisation
If a user opts out of ads personalisation using Google's Ads Settings, they will no longer receive personalised advertising from Google.
When does AdSense send cookies to a browser?
AdSense sends a cookie to the user's browser after any impression, click or other activity that results in a call to our servers. If the browser accepts the cookie, the cookie is stored on the browser.
Most commonly, AdSense sends a cookie to the browser when a user visits a page that shows Google ads. Pages with Google ads include ad tags that instruct browsers to request ad content from our servers. When the server delivers the ad content, it also sends a cookie. But a page doesn’t have to show Google ads for this to happen; it just needs to include our ad tags, which might load a click tracker or impression pixel instead.
Notify users about cookies
Third-party and first-party cookies
Cookies are categorised as third-party or first-party depending on whether they're associated with the domain of the site that a user visits. Third-party cookies are associated with a domain that's different from the domain of the site that a user visits. The third-party cookies used by AdSense for advertising purposes may be associated with the doubleclick.net or country-specific Google domains such as google.com. Note that this doesn't change the name or content of the actual cookie. The difference between a third-party cookie and a first-party cookie is only a matter of which domain a browser is pointed towards. An identical cookie might be sent in either scenario.
Custom Search Ads (including AdSense for Search, AdSense for Shopping and Programmable Search Engine) also uses a combination of first-party and third-party cookies. First-party cookies are relied upon primarily when access to third-party cookies is restricted, and are required to continue ad serving.