Software repositories such as source control systems, defect tracking systems, and archived communications between project personnel are used to help manage the progress of software projects. Software practitioners and researchers more and more recognize the potential benefit of mining this information to support the maintenance of software systems, improve software design/reuse, and empirically validate novel ideas and techniques. Research is now proceeding to uncover the ways in which mining these repositories can help to understand software development, to support predictions about software development, and to plan various evolutionary aspects of software projects.