The National Library of Iceland – University Library has implemented an international numbering system for sheet music and sheet music-related publications, ISMN, International Standard Music Number. The ISMN system is a sister system to the international book numbering system ISBN and works in the same way.
Publishers of sheet music or music books may apply for serial numbers with their publisher number or individual ISMN numbers for individual publications. Publishers that have been assigned ISBN serial numbers are asked not to use ISBN numbers for sheet music or music books but to apply for ISMN numbers for such publications. If a music book has been assigned an ISBN number, the ISMN number should be used if it is reprinted or reissued. ISMN numbers may be assigned retroactively and, if desired, can be reversed.