What is the IEC 62443 series designed for, which fields refer to it, and which field uses its own standard instead?

It is designed for industrial automation and control systems (IACS), with parts for system integrators and operators and parts for product developers. Railway, medical and aviation guidance refer to it. Automotive uses ISO/SAE 21434 instead.

IEC 62443 grew out of the industrial world, but it is the most complete public framework for building secure components, so other fields borrow it:

• Railway: CLC/TS 50701 builds on it.
• Medical: the FDA's cybersecurity guidance and MDR/IVDR guidance refer to it.
• Aviation: IATA guidelines refer to it.

Its parts are split by audience. Asset owners, operators and system integrators use the 2-x and 3-x parts. Product developers use 4-1 (the secure development process) and 4-2 (technical requirements per component). The automotive industry is the notable exception: it has its own lifecycle standard, ISO/SAE 21434.

Go deeper:

• ISA — ISA/IEC 62443 series of standards — which part is written for which role
• IEC 62443 (Wikipedia) — structure of the series and its adoption