This chapter faces the problem of identifying a set of parameters characterizing COTS products. The need for this characterization derives from the problem to identify and select among many available products the ones which are appropriate for a specific software system. The characterization has the goal to foresee the integration and maintenance effort in COTS based systems developed with a COTS-based approach. In our study we propose a set of COTS product parameters and perform an empirical study in the context of two industrial software projects to assess these parameters. The assessment aims at finding any statistically significant correlation among the proposed parameters and the effectiveness of development and maintenance process. The obtained results show that our COTS products characterization can be used to foresee integration and maintenance effort of the COTS based system. The analysis also shows the need to continue the on-field experimentation, in order to make the learned lessons effective and applicable.