Only in the very last years of his life did Nielsen turn his attention to organ music. His neglect of the instrument may have had some correlation with the fact that he largely avoided the church throughout his lifetime, for otherwise, his contrapuntal gift ideally suited him to it. Nevertheless, he was close with Emilius Bangert, organist of Roskilde Cathedral, and his friend's encouragement no doubt had something to do with his decision to write the 29 Little Preludes "for organ or harmoium," which were published in 1930 as his Opus 51.

Nielsen found models for these little preludes—which at most comprise 30 bars in length each—in the classic organ music of Bach, Frescobaldi, Pachelbel, and Scheidt, among other Baroque masters. Their extreme brevity notwithstanding, these are strikingly varied works in aspects of texture, form, harmonic language, and expression.

The beginning of Prelude No. 3 is made up of simple chord progressions, while others bear strange sequences and modulate into remote keys before ending up in the original key. Still others (such as Prelude No. 2) begin as a fugue with a unison theme only partially imitated by the following voices. Stylistically, the preludes range from the graceful and lyric, to the capricious and dramatic, to occasionally solemn and grand. There is a certain unfinished quality to many of the preludes, as the composer has given scant hints as to registration, dynamics, tempo markings, and so forth. In his study of the collection, Finn Viderø suggests that "One gets the impression that these peices were not written for us but were made for his own sake. They are studies in organ texture with the purpose of trying out the various possibilities of the instrument."

© Brian Wise, All Music Guide