The criteria for evaluating the architecture of COTS based software systems is different from the criteria used for custom-built software systems. These differences arise due to the different development and maintenance scenarios that are the business drivers for COTS based software systems. Current architecture evaluation methods must be adapted to take these differences into account. One approach is to use the Architecture Tradeo. Analysis Method^SM (ATAM^SM) as a basis for the evaluation. This can be done by identifying the Scenarios and Utility Trees that are applicable to COTS based software systems.