Abstract This paper provides a systematic approach and summary of mathematical tools to analyze and estimate the impact of Built-In-Test (BIT) design parameters on systems reliability, availability and maintainability (RAM). Simple cases are presented to show that the approach is reasonable and comprehensive to provide a foundation for the optimization of system RAM with BIT. This optimum selection of BIT parameters during systems design is extremely important because, if BIT parameters are not selected correctly, the system RAM will be deteriorated. So the designers must pay attention to the effect of BIT parameters during the system design phase. Although BIT is an extremely important component in the design of complex systems, the definitions relative to BIT parameters and the methodology for analyzing BIT is not well defined in a consistent fashion in the literature. This is not a criticism but is simply due to many different industrial and military organizations working on BIT systems while accepted standards on notations and analysis procedures have not yet clearly evolved. This is not unusual for a new and developing methodology that is application driven. This paper provides a consistent, comprehensive and thorough overview of BIT as it relates to system RAM.