Software Reliability is defined as the probability with which the software will operate without any failure for a specific period of time in a specific environment. It is one the essential software quality features. Software reliability estimated in early phases of software development life cycle saves a lot of time and money as it prevents spending huge amount of money on fixation of defects in the software after it has been deployed. Software reliability estimation has thus become an important research area as every organization aims to produce defect free software. There are many software reliability growth models that are used to assess the reliability of the software. These models help in developing robust and fault tolerant systems. This paper presents a review of optimization techniques used by many researchers on the software reliability growth models in order to estimate the software reliability effectively.