Many software reliability growth models (SRGMs) based on nonhomogeneous Poisson processes (NHPP) have been developed in the past three decades to predict the reliability of software systems and the remaining faults in the software. The underlying common assumption of many existing models is that the operating environment and the development environment are the same. This is often not the case in practice because the operating environments are usually unknown due to the uncertainty of environments in the field. In this chapter, we provide a state-of-the-art summary of software reliability models in the literature. We also discuss recent developments in model selection criteria that can help practitioners choose an appropriate software reliability model.