31, by Louis Vierne for organ or harmonium were written in two volumes during the years 1913 and 1914.

It is a collection of pieces for organ or harmonium, of medium level (intermediate), with an indication by the author of registrations and nuances.

Vierne wrote in the Durand edition: The parts of this collection are calculated in such a way that they can be executed during the normal duration of an Offertory.

Two immediately adjacent initials (G. R.) indicate that the grand organ is coupled to the récit, or swell; the initial G. indicates that this keyboard is separated from the swell.

These pieces follow the same pattern of keys that Johann Sebastian Bach used for his two volumes of The Well-Tempered Clavier.