Instability is the nature of any application. An Application may strive for and helps a business or company for some time (may be 10 or 15 years), during that time it has been corrected, adapted and enhanced many times. But every time a change is made into the application, unexpected and serious side effects occur. Yet the application must continue to evolve. Unmaintainable software is not a new problem. In the following sections, we are going to analyze the Software Re-engineering and Reverse-engineering processes and how they help any application to maintain the Quality standards.

Keywords: Instability, Re-engineering, Reverse-engineering, Software, Quality.