Over last three decades many Software Reliability Growth Models (SRGMs) have been proposed for estimation of reliability growth of products during software development process. Each model could be shown to work well with a unique data set, but no model appeared to do well on all data sets. Now the question is which model we should use? Selection of optimal SRGM for use in a particular case has been an area of interest for researchers in the field of software reliability. Till now, there is no such method that takes the weight of comparison criteria in selecting the appropriate model. All existing methods consider each comparison criteria with equal priority. But in real scenario, different criteria have different impact in measuring the software reliability. In order to remove this flaw, this book presents a technique known as "Weighted Criteria Method" for optimal selection of SRGMs. Weighted criteria method uses the weight of each criterion to calculate the overall value of the model or model permanent value. These values of models are used to compare and rank the models.