You are probably running multiple AdWords campaigns. One of the keys to success with AdWords is to have a few closely related keywords in an Ad Group. The Free AdWords Strategy Guide recommends only one keyword per Ad Group. This allows you to have a very relevant ad and landing page for your keyword. Many marketers follow this advice having many, many Ad Groups with only one or a few keyword in each. You may have these Ad Groups spread across a couple campaigns.

Multiple campaigns can create problems. That problem is duplicate keywords. You must very careful not to duplicate keywords across different campaigns.

You will be bidding against yourself. For example, say you have a keyword in campaign A and campaign B. In order to campaign B to have it's ad in the top position, it's going to have to out bid campaign A.

Second, you are damaging the CTR of both campaigns, which damages the quality score and results in higher CPCs. On a search for the keyword, both the ad from campaign A and B will appear. Both campaigns will receive an impression. The best possible outcome of the impression is to have the consumer click your ad. However, the consumer cannot click both ads. The consumer will either click A or B. You will have at least one impression without a chance for a click through. You are automatically cutting the CTR in half.

How do you check for duplicate keywords? The AdWords Editor software can help you determine if you have duplicates. There is a check for duplicate keywords across Ad Groups. The Editor will assist you in finding any duplicates that you do have.

The bottom line is that you need to check and make sure you aren't bidding against yourself.