To clarify "they" don't actually care who your identity is. While it is really important to you, knowing that you are John Smith of 123 Main Street isn't that

To clarify "they" don't actually care who your identity is. While it is really important to you, knowing that you are John Smith of 123 Main Street isn't that useful to them. Knowing that "you" (your browser) looked at buying a car last week is far more valuable, especially when combined with other activity and demographic guesses. ie rather than a solid individual, your database records are a set of probabilities. Looked at diapers - probably have a kid. Looked at concert tickets for One Direction - you are likely young and very unlikely old. Combine all these anonymous snippets and probabilities and the database representation of you is then "exploited". The goal is relevancy. Advertising pays on results, which means the advertisers don't want to pay for things going to people that aren't the targets. eg if they have a campaign aimed at females 20-30 years old that have children in North Texas, then they aren't going to pay for ads going to 60 year old men in Seattle. And if it is a car company, then ads going to people who are likely to buy a car in the near future is far more valuable than a kid playing Angry Birds. (There is also brand advertising where the idea is to keep a brand in your head and good feelings about it, but no immediate action expected of you. They find out if this works by doing it in some areas and not others, and then tracking sales etc over the longer term.) In theory this should lead to you get good relevant to your interests advertising. In practise it is annoying drivel to many because the companies advertising (ie the ones paying) aren't relevant to you. They are trying to get your attention. While I only mention advertising, the other pieces especially tracking are pretty much in support of the advertising. It allows the probabilistic deductions about you. To avoid this you would need to eliminate Internet activity, or go completely anonymous (eg only using Tor, incognito browser sessions, and have components on your system constantly make up data like user agents and locations). BTW you can see what Google has guessed about you at https://www.google.com/ads/preferences/ https://www.google.com/ads/preferences/ which works even if you aren't signed in.