What’s the difference between A 'Type A' and 'Type B' MSS?

A Type A MSS contains requirements against which an organization can claim conformance, whereas a Type B MSS does not. 

As a consequence, one should only find recommendations (guidelines) or supporting information in a Type B MSS. Some MSSs can contain a mix of requirements and guidelines: as they contain requirements, they will be considered Type A MSSs. Usually, a Type B MSS (e.g. ISO 50004) provides guidance on the application of a Type A MSS (e.g. ISO 50001). However, some Type B MSSs are independent (e.g. ISO 19600).

Management Standards (MS) support governance and leadership functions, at all levels. They are designed to be widely applicable across economic sectors (or specific to some), various types and sizes of organizations and diverse geographical, cultural and social conditions. MS can be considered as overarching documents for the sound governance of an organization. Using MSS can be a practical way of supporting decisions resulting from the implementation of a MS.

To claim conformance with a standard, an organization needs evidence that it is meeting the requirements. Such evidence gathering is generally done by undertaking an audit. There are three types of audits: first-party, second-party, and third-party. First-party audits are internal audits. Second and third party audits are external audits. A third party audit can result in certification. Regarding certification: certification can only take place against a document that contains requirements. Therefore, Type B MSS cannot be certified against. 

High Level Structure - HLS

Standards listed here as HLS have the same structure [PDF] and contain many of the same terms and definitions. This is particularly useful for those organizations that choose to operate a single (sometimes called “integrated”) management system that can meet the requirements of two or more management system standards simultaneously.