The Institution of Mechanical Engineers has stated, and the British Standards Institution has accepted, that a standard should reflect both the most up-to-date and reliable advice that can be applied within prevailing economic restraints, and the needs of supplier and user. The paper reviews some features of safety valve design from 1680 onwards and relates these to various requirements of British Standards for safety valves, BS 759 of 1937, and its subsequent revisions, BS 1123 of 1943, and its revisions, both of which are application standards, and BS 6759: 1984, which is a product standard. This latter standard for safety valves, which is in three parts, (Part 1. Safety valves for steam and hot water; Part 2. Safety valves for compressed air and compressed inert gas; Part 3. Safety valves for process fluids not covered by Parts 1 and 2) is introduced and described in some detail, particular attention being given to the sections dealing with the certification of performance of any given design.