Do you have a website and using both AdSense and AdWords? If so, this post will interest you. You may start by looking at the attached picture.
AdWords and AdSense are the different sides of the same coin and Google is in the middle, biting on the metal. AdSense allows website owners to show different ads from different advertisers on their website and receive revenues for it. AdWords allow you to advertise your website on many other websites running AdSense. Google takes its commission for providing both these services. Though many other competing programs exist on the web, Google's generally have good reputation.
Advertising my site on my site?!?!?!
This morning, I was amazed to see an ad to my website for collectors on the same site! Had I clicked this ad, my AdWords account would have been billed for the click while my AdSense account would have received some revenue. Obviously the latter would be lesser since Google get their cut. This is, of course, ridiculous and should be automatically prevented by Google. Apparently, it isn't. Just to ensure you that I'm not an idiot, the ad is for colnect.com and the website is on the same domain - colnect.com
I usually view my own site with ads disabled so I don't accidentally click an ad and violate the terms of service. This time I was at a friend's house and am quite happy to have stumbled upon the aforementioned bug/feature.
Both accounts allow you to use filters and I've now added "competition filters" for my AdSense account that will prevent showing ads for any of my domain. It's also possible to filter out sites on AdWords but this can seemingly be done only on the campaign level so if you're running many different campaigns, it'll become tedious. See the attached pictures.