Enterprises start application rationalization initiatives, but after the low-hanging fruit of little used business applications, they find it a struggle to progress. There are many root causes underlying this challenge — from determining what the target should be and overcoming business objections to acquiring sustained funding. Exacerbating this challenge is a lack of metrics that show progress and value and maintain executive interest. The metrics you should choose for your application rationalization program should reflect a balance of business concerns that, when taken together, guide business decision-making. This report, the fourth in a series on application rationalization, describes how to identify the metrics that matter.