Capitalization of key, opus, and number

Music Cataloging at YaleLanguage tools

Note: These instructions apply to recording information for title and contents notes in bibliographic records and 670 field in authority records. They do not apply to authorized access points for music.


See also The names of keys in French, German, Italian, and Spanish

  • In English, the key is capitalized, but not the mode: A major, D minor.
  • In German1, D in Dur and M in Moll are capitalized.
    • In major, the key is capitalized: D-Dur, Fis-Dur
    • In minor, it is not capitalized: a-Moll, fis-Moll
  • In other languages,
    • when given as a letter, the key is capitalized: F majeur, G mineur
    • but when given as a word, it is not capitalized: fa majeur, sol mineur.
  • Symphonie Nr. 2 C-Dur op. 61
  • Konzert für Violoncello und Orchester a-Moll, op. 129
  • Messe in Es op. 155
  • Concerto in A minor (Wq 166, H 431) for flute, strings and basso continuo
  • Sonata per cembalo in sol maggiore
  • Koncert C dur2 pro fagot a smycce

The LC Music Division's Bibliographic Access Section's policy regarding transcription and recording of statements of key that are in German:

  • The words "Dur" and "Moll" will always be capitalized.
  • Letters and initial letters with suffixes indicating flats and sharps (-is, -es) will be in upper case when preceding "Dur" and in lower case when preceding "Moll".

Source: e-mail on NMP-L from Damian Iseminger, Head, Bibliographic Access Section, Music Division, Library of Congress, dated 10/11/2018

1This policy is based on a 1977 LC memo stating that, regardless of how a word appears on the publication, for German capitalization, follow Duden Rechtschreibung der deutschen Sprache und der Fremdwörter (Mannheim : Bibliographisches Institut, c1986) It is unknown if LC is applying this policy in RDA
2D in dur is not capitalized here because it is not in German.


  • In German1, opus is capitalized when spelled out, but not when abbreviated: Opus, op.
  • In other languages, neither is capitalized.
  • Vier Fugen Opus 72
  • String trio opus 45
  • Symphonies Nr. 2 C-Dur op. 61
  • Quartet op. 73 for 2 violins, viola, and cello


See also The names of numbers in French, German, Italian, and Spanish

  • In German1, number and its abbreviations are capitalized: Number, Nr., No.
  • In other languages, it is not: number, no., nr.
  • Duo concertant für zwei Klarinetten op. 3, Nr. 1
  • Fantasie für Klavier ohne D-Nummer = Fantasy for piano without "D" number
  • Quartet No. IV für 2 Violinen, Viola & Violoncello, op. 40
  • Sonata in D major op. 2 no. 2