ROI - Return on Investment - is a commonly used term but one that is often not measured effectively by advertisers who are running PPC campaigns, or any form of marketing for that matter.

The Inside AdWords blog, from Google, is posting a series of articles looking at ROI. The first piece , written by 'guest contributor' Fred Vallaeys, presents an overview of the issue, defining what ROI is and why it should be measured. It's a good, clearly written introduction to the subject and one that all PPC advertisers should read and then do something about!