How does Google Analytics handle cookies?

Google Analytics uses only 1st party cookies which are considered to be safe and nonintrusive by most browsers. Many people will block 3rd party cookies when setting their browser configurations however this will not impact Google Analytics reporting.

When does Google Analytics tracking not work?

If a user blocks all cookies in their browser then Google Analytics will be affected and will not be able to track that user. If a visitor to the site has disabled Javascript in their browser (or a mobile user has javascript disabled), they will not be tracked by Google Analytics. In addition, if there is an Javascript error on the page before the Google Analytics code has run, data will not be tracked for that sessoin. The error prevents the remainder of the Javascript to load on the page and since Google Analytics code is placed in the footer, it will not run.

When a user deletes their cookies there is no way of knowing whether they have been to the site upon a subsequent visit and they will be tracked as new visitor.

Google does not track any personally identifiable data on users. All data collected by Google is anonymous. Google does not share any data with 3rd party sources.