A Safety Integrity Level (SIL) (or a variety of other similar terms and concepts in various safety standards) provides a means of specifying the integrity required when developing a product in order to make it acceptably safe.

A Safety Integrity Level loses meaning if the relevant safety requirements do not define what is required of the system.

A large number of references to SILs are in safety-critical software, where the SIL plays a part in translating a quantitative goal into qualitative goals, usually changing product requirements into process requirements. This is mostly due to difficulties in analysing or testing complex systems (usually software) to the point where valid and useful quantitative statements can be made, instead relying upon evidence of adequate development processes.

• In AS 61508 "Functional safety of electrical/electronic/programmable electronic safety-related systems", SILs affect the design and implementation of both hardware and software. Higher levels in hardware require certain minimal architecture redundancy and component reliabilities. Higher levels in software require the application of more robust specification, analysis and testing techniques.
• Def(Aust) 5679 "The Procurement Of Computer-based Safety Critical Systems" places particular emphasis on the use of formal methods where a high Level of Trust is required.
• In RTCA/DO-178 "Software Considerations in Airborne Systems and Equipment Certification", a higher Software Level requires greater general rigour, process evidence, testing and level of independence of various activities. For example, Software Level C requires statement coverage whereas Software Level A requires modified condition decision coverage (MCDC) when conducting testing.