There is a widespread demand for evidence about the impact and benefits of process improvement based on Capability Maturity Model Integration (CMMI) models. Much has been documented about the practice of CMM-based process improvement and its value for the development and maintenance of software and software-intensive systems; however, the existing information is sometimes outdated and there are increasing calls for evidence directly based on CMMI experience. This special report presents selected results from 12 case studies drawn from 11 organizations. While still limited, the case studies provide credible evidence that CMMI-based process improvement can help organizations achieve better project performance and produce higher quality products. The report also describes plans for gathering further evidence from organizations using CMMI models.