The Harmonized Structure is the common framework — identical clause numbering, common text and shared terminology — used across ISO management system standards. It is defined in Annex SL of the ISO/IEC Directives Part 1.
The naming, which trips people up
It was called the High Level Structure (HLS) until the 2021 twelfth edition of the Directives, when it was renamed the Harmonized Structure. Annex SL is still the correct name of the annex; HLS is not the correct name of the structure.
Using “Annex SL high level structure” pairs a current container with a term retired five years ago. Minor, but it is the sort of detail a technical audience notices.
The structure
Clauses 1 to 3 cover scope, references and terms. Clauses 4 to 10 carry the requirements: Context, Leadership, Planning, Support, Operation, Performance evaluation, Improvement.
Why it matters commercially
Because ISO 9001, 14001, 45001 and 27001 share this skeleton, an organisation certified to one has already built much of another. Context, leadership, competence, documented information, internal audit, management review and improvement are substantially common.
An integrated build, and a combined audit, can be materially less work than running the standards as separate projects. The saving is real enough that adding a second standard is often the cheapest quality investment available to an already-certified organisation.
What does not transfer is the technical core — clause 8 differs sharply between standards, and ISO 13485 and ISO/IEC 17025 sit further outside the pattern.