IEC 60987:2021 provides requirements and recommendations for the hardware aspects of I&C systems whatever the technology and applies for all safety classes in a graded manner (as defined by IEC 61513). The requirements defined within this document guide, in particular, the selection of pre-existing components, hardware aspects of system detailed design and implementation and equipment manufacturing. This third edition cancels and replaces the second edition published in 2007. This edition includes the following significant technical changes with respect to the previous edition: a) Title modified; b) Take account of the fact that hardware requirements apply to all I&C technologies, including conventional hardwired equipment, programmable digital equipment or by using a combination of both types of equipment; c) Align the standard with the new revisions of IAEA documents SSR-2/1, which include as far as possible an adaptation of the definitions; d) Replace, as far as possible, the requirements associated with standards published since the edition 2.1, especially IEC 61513, IEC 60880, IEC 62138, IEC 62566 and IEC 62566‑2; e) Review the existing requirements and update the terminology and definitions; f) Extend the scope of the standard to all hardware (computerized and non-computerized) and to all safety classes 1, 2 and 3; g) Complete, update the IEC and IAEA references and vocabulary; h) Check possible impact of other IAEA requirements and recommendations considering extension of the scope of SC 45A; i) Highlight the use of IEC 62566 and IEC 62566-2 for HPD development; j) Introduce specific activities for pre-existing items (selection, acceptability and/or mitigation); k) Introduce clearer requirements for electronic module-level design, manufacturing and control; l) Complete reliability assessment methods; m) Introduce requirements when using automated tests or control activities; n) Complete description of manufacturing control activities (control process, assessment of manufactured equipment, preservation of products); o) Define and ensure the inclusion of a graded approach for dealing with the 3 different classes of equipment and related requirements.