Recently, complexity and interaction of electrical, electronic and programmable electronic (E/E/PE) systems increase, a growing emphasis has been placed on the concept of functional safety during product development. IEC 61508 is called a mother standard for functional safety that provides guidelines and standardized procedures in the development of reliable and dependable E/E/PE systems to assure functional safety. Determining risk classes (i.e., SILs(Safety Integrity Level) or ASILs(Automotive Safety Integrity Level)) associated to a specific E/E/PE item may be recognized as one of the most crucial activities in the product development per IEC 61508, ISO 26262, ISO 13839, ISO 15998 or IEC 61511 etc., since SILs or ASILs are used to specify necessary safety requirements for achieving an acceptable residual risk. This paper is focused on introduction the international standards for functional safety which are based on IEC 61508 and ISO 26262.