This chapter takes the the view that there exist several components and aspects of software reliability and they need to be integrated into a systematic framework. It presents the essential concepts and approaches needed for predicting, evaluating, and managing the reliability of software. The chapter also presents the type of tools available for assisting in achieving and evaluating reliability. Software controls everyday life of individuals involving commerce or social interactions, in addition to critical applications such as aviation or banking. Reliability growth in software is generally described using a software reliability growth model. As bugs are encountered and removed during testing, the reliability of the software improves. In hardware systems, the reliability gradually declines because the possibility of a permanent failure increases. During debugging, the objective of software testing is to find faults as quickly as possible and remove them to increase the reliability as fast as possible.