You might wonder how does Google target ads on a particular website. The knack of adsense is that  Ad’s are shown automatically without having to choose them. It’s done in three different ways.

Contextual targeting

Adsense spiders visit your site and scan every page it learns what the content is about. And matches ads as per content of the pages. In doing this, they consider few things like a keyword used and its density, font size, link structure and also the website color scheme if you optioned to display image ads.

Placement Targeting

Placement targeting allow the advertiser to place their ads on the specific place. He can choose to place an ad anywhere he wished and on any website, which is displaying Google’s ads. This is usually done on a niche based site.

Interest Based Advertising

Interest based advertising allows an advertiser to reach users as per their interest like finance, technology, etc. And allows them to show ads based on a user’s previous interactions with them like filling any form or subscribing to their service, etc. To support the Internet based advertising Google offers Ads Preferences Manager ( http://www.google.com/ads/preferences/ ) to their users to view and edit interest categories. They do this by storing a cookie on your computer, which has the information about your interest and next time you visit any site, which has adsense ads, it will show the ads related to your interest.

Quick Tip: Google’s ad preferences manager use cookie to target ads, once the cookie is removed you won’t be able to ads as you selected in category.