Software Reliability Engineering quantifies the software failures. Software failures may be due to errors, ambiguities, oversights or misinterpretation in the Software Development. Thus the reliability of software is compromised by system failures. The Software Reliability Growth Model (SRGM) is a tool, which can be used to evaluate the software quantitatively, develop test status, schedule status and monitor the changes in reliability performance. Software Reliability models have been developed to estimate the fault content, failure rate and fault removal rate per fault in software and to predict the reliability of the software at the release time.