 In this chapter we discuss the current trends and challenges that arise in the COTS-based requirements engineering. When acquiring COTS products, customers are put into unexpected situations over which they have no control. Therefore, requirements have to be more flexible in order to meet the products constraints. We point out the main research efforts that have been done to support the COTS-based requirements process and discuss the advantages and drawbacks of each proposal. We argue that the matching process between products’ features and users requirements is a fundamental issue to be treated during the evaluation process. In this context, we propose a goal-oriented approach to identify mismatches and deal with conflicts.