This document applies in case a CIUS is produced as a specification with the objective of registering it in the appropriate registry. This document also establishes requirements for the steps to be taken in the process of creating Core Invoice Usage Specifications (CIUS) as defined in EN 16931-1. Furthermore this document provides guidance for the creation and implementation of a CIUS. The following points are the focus: steps that need to be taken in consideration to avoid unnecessary proliferation and fragmentation in the use of CIUSs; guidance on the creation and implementation of CIUSs, with a quality control objective. It should be noted that it is planned to apply the same principles and processes to extensions that are documented in a separate document.