The Catalogue of Carl Nielsen's Works (CNW) is the first ever thematic-bibliographic registration of all Nielsen's compositions. A few catalogues have previously been prepared of which Fog and Schousboe'sDan Fog and Torben Schousboe: Carl Nielsen. Kompositioner. En Bibliografi. Copenhagen 1965 bibliography (1965) was the first. Also the Bjørnum and MøllerhøjBirgit Bjørnum and Klaus Møllerhøj, Carl Nielsens Samling. Katalog over komponistens musikhåndskrifter i Det kongelige Bibliotek. Copenhagen 1992 description of Nielsen's manuscripts in The Royal Danish Library (1992) is one of the most important groundworks. Strictly speaking, however, none of these are catalogues of works. Their numberings are mainly related to bibliographical items – prints (FS) and manuscripts (CNS), respectively. Though they may to some degree serve as work catalogues, there is no strict one-to-one relationship between compositions and the catalogue numbers. For instance, FS numbers song collections (i.e. publications) rather than the individual songs; therefore, a single song may have as many as four different FS numbers, none of which can be used to identify the particular song.

The first complete survey of all Nielsen's compositions and their sources was not initiated, however, until the foundation of the The Carl Nielsen Edition (CNU; completed 2009) Carl Nielsen Udgaven. The Royal Library: Copenhagen 1998–2009 . In more than one sense, CNW is a natural extension of CNU and builds to a large degree on information accumulated in connection with the editing project and to a certain extent also in connection with other projects. The information has been rectified when the editors either have been aware of or had their attention drawn to errors. However, due to limited resources the editors have not been able to verify all information systematically. Original sources have only been consulted in cases of doubt.

The Danish Centre for Music Editing which is responsible for the publication of CNW was established at The Royal Danish Library shortly after the completion of the Carl Nielsen Edition in order to maintain and carry on the music philological expertise and not least exploit the detailed knowledge of Nielsen's works that had been gathered during the working on the complete edition.

Biographical as well as bibliographic information has also been drawn from a number of other sources, among others Nielsen's lettersJohn Fellow (ed.), Carl Nielsen Brevudgaven. Copenhagen 2005–2015.
A selection in English translation is published in:
David Fanning and Michelle Assay (eds.), Carl Nielsen. Selected Letters and Diaries. Copenhagen 2017
, the publication of Nielsen's essaysJohn Fellow (ed.), Carl Nielsen til sin samtid. Copenhagen 1999 , the publication of Nielsen's essaysJohn Fellow (ed.), Carl Nielsen til sin samtid. Copenhagen 1999 , and the current bibliography available in the journal, Carl Nielsen Studies , all affiliated with The Royal Library.

A book version of the catalogue is available from Museum Tusculanum Press

We wish to express our sincerest thanks to Carl Nielsen og Anne Marie Carl-Nielsens Legat (the Carl Nielsen and Anne Marie Carl-Nielsen's Foundation) for financial support of the project. Thanks are also due to Knud Ketting who most kindly has provided us with information on known performances of the musical works.

The Danish Centre for Music Publication collaborates with Carl Nielsen 2015 .