An introduction to IEC61508: free brochure
For a very general introduction to IEC61508, there’s a long-serving but decent enough downloadable brochure on the IEC website. Simply titled Functional safety of electrical/ electronic/ programmable electronic safety-related systems, the 12-page document is a good management-level backgrounder and lists all the full IEC61508 specification documents. You can download a copy of the IEC61508 brochure here (PDF, 524kB).
