This link posts the highest paying keywords in the Google AdWords service. The poster has mistaken AdSense for AdWords, but I'll forgive him. It's amazing how expensive the CPC (cost per click) can be! The search phrase "tax attorney" is $45.55. If I understand this correctly, you sign up for a word or a phrase and when somebody searches for that in Google, your ad is among the others who have also signed up for that word/phrase. And then, if that user clicks on your ad, you have to pay Google that CPC value. No wonder it's estimated that Google makes billions of dollars in revenue.