The ISSN is an identification system intended to reliably identify serials and other on-going resources worldwide. ISSN assignment is ensured by a Network of 89 national centres, coordinated by the ISSN International Centre. National Centres are also in charge of producing the bibliographic records describing the resources, records which are ingested in the ISSN Register. To that end, they follow the rules expressed in the ISSN Manual, which depends on one hand on the ISSN Standard (ISO 3297) and on the other hand on the ISBD. As the characteristics and boundaries of continuing resources are constantly evolving, especially on a digital form, the maintenance and the evolution of the Manual is a critical task. It is ensured by the ISSN Review Group, composed of experts from various National Centres. This group also provides support and advices to all National Centres. Finally, the ISSN RG aims to be involved in the evolution of the main bibliographic models, cataloguing codes (ISBD and RDA) or formats, at national and international levels, and to promote there the recognition of the unique characteristics of continuing resources.