Sources: The primary source is a microfilm called Columbia Classification Scheme dated 1942 and kept in SLS Library (microfilm F74). This is a difficult document. The original was not a unified schedule but a collection of mostly typewritten papers which appear to be those used in the Cataloging Dept. Some information is presented twice with unexplained variations and some is missing. In a few spots it is not clear which call numbers are used in General Library and which in departmental libraries, or which of several tables is for General Library. In compiling the schedules and notes following, I referred extensively to the shelflist to clarify, correct and expand on the information in the microfilm material. Reference to past practice as shown in the shelflist was always required. I found that I was compiling the only concise description of the scheme ever written. Coverage: The schedules in the present document refer only to the General Library. Of the other libraries, the Burgess, Carpenter, Classics and College libraries followed closest to General Library. Philosophy Library differed in classifying works of Philosophy, and the other libraries differed in various ways. SLS Library was alone in using true Dewey Decimal Classification (although with D prefix). The Reference Dept still uses its version of Columbia Classification. Letter prefixes: In general, call numbers without letter prefixes are in General Library. At one time the following exceptions existed: 343-349 Law Library, 370-379 Teachers College Library, 500-699 various science libraries, 780-789 Music Library. The letter prefix L was used to designate General Library books in those classes, except 780-789 for which there were apparently never any L780-L789. At the present time, Law and TC call numbers do not appear in the General Catalog, Music Library's 780-789 have been reclassed, and 500-699 have been shelved in General Library (level 2 Annex) or marked "Science" in the catalog. The only remaining exception is 510-519, with none in General Library, so the L prefix is no longer significant. Other prefixes: All other prefixes designate non-General Library books. The major ones are: D : Departmental Library. R : Reference Dept. B : Rare Book. LS : Library Service reading room. DG is part of Classics (Burgess-Carpenter) and the several others are Rare Book Library special collections. All are significant, although D does not signify enough. The prefixes seem to be dropped from most automated catalog records, so they do not match the books' markings. Terminology: This is an old classification schedule, and I have preferred the wording of the original even though it is outdated in various places. In brackets  I have occasionally supplied modern terms or explanatory phrases, but some antique terms are left as is. A few very long entries are shortened, and some important subtopics are mentioned here with the main call number.