The National and University Library of Iceland have recently implemented an international numbering system for notated music, ISMN, the International Standard Music Number. The ISMN is analogous to the International Standard Book Number, ISBN, but serves as a unique identifier for notated music. Icelandic music publishers are encouraged to familiarize themselves with the ISMN system and advised not to use an ISBN for notated publications. Publishers can apply for publisher prefixes or a single ISMN. The ISMN is compatible with the EAN 13-digit barcode.