This paper provides an overview of the development of standards and guidelines for safety critical systems over the past 35 years. In the context of this paper “safety critical systems” refers to those systems that are intended to achieve, together with the other risk reduction measures, the necessary risk reduction to meet the required tolerable risk. The period covered by the paper is from the time that concerns were raised about the adoption of programmable electronic systems for implementing safety functions to today. It is essentially a personal account based on experience and reflections of the developments have taken place with to respect of guidelines and standards and is not intended in any way to be an authoritative account covering all industrial sectors.