I recently noticed a so-called "I-Catalogue Number" in the General information section of scores on IMSLP, such as this score. What does this mean? I searched on IMSLP and on the internet, but could not find the explanation.


The unanswered question by Charles Ives has the I-Catalogue Number ICI 16 on IMSLP. This number is also mentioned on a recent CD [click on Tracklisting].

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    I havent a clue but do note that the two letters after the "I" are the composer's initials. E.g. IJH for Joseph Haydn in the one you linked to.
    – Ian Cook
    Feb 4, 2018 at 17:45
  • @IanCook Indeed, therefore I started thinking that it is maybe an internal numbering defined by IMSLP (I for IMSLP and 2 letters for the composer)?
    – Karlo
    Feb 5, 2018 at 1:05

1 Answer 1


By an answer provided on the imslp forums, it seems to be an internal numbering, without any particular order or meaning:

b) IMSLP is the authority on I-Catalog numbers, but any composer is welcome to create his/her own catalog system (e.g. opus numbers).

c) To keep things simple the only promise is that the numbers are unique and stick with the page. The numbering is not intended to be chronological, rather, the initial assignment is ordered alphabetically. Sometimes this becomes chronological (e.g. Symphony No.1 through No.30 or something), but that's not the intention. Newly added pieces are assigned the next available number.

d) The intention of the I-Catalog system is as a fallback to uniquely identify pieces where there is no authoritative catalog system. It is not intended to be musicologically sophisticated or to replace a well-researched catalog.

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