The AdWords Impression Share Report tells you the percentage of times your ads were actually shown compared to the total number of times your ads could have been shown. Google introduced it some time ago as a share of market/ share of voice measurement. While it is not an easy report to fully understand it does give useful information which allows for more targeted and successful Campaigns.

Impression Share Report

The Impression Share Report can be created in the AdWords Report centre. The report shows the Impression Share(IS) for the Campaign and the percentage lost due to either the budget being too low, Lost IS (Budget) or lost due to poor ranking, Lost IS (Rank). For most Campaigns the largest loss has to do with Rank.  As Rank is CPC X Quality Score the most cost effective way to improve is to improve Quality Score.

Given that not all of the keywords in the Campaign will have a great Quality Score and your Maxm CPC will not always be high enough it is very unlikely that you will get 100% Impression Share (IS).  One reason for low IS could be that the keywords are not showing up on broad match. The Exact match (IS) figures helps here as they show how the Campaign would perform IF all keywords were Exact Match. Increasing your bid will also improve your Ranking too. However in chasing greater Impression Share remember that 30% or 40% Impression Share of a large `market` is better than a 100% IS of a small market. So do not be afraid to keep less than optimal keywords in the Campaign.

One drawback of this report is that it is only available at the Account and Campaign level where there is often too much data to make sense of it all. If this report was available at the ad group level I think it would be more widely used.