In point of chronological sequence, this edition is the fifteenth. To name it the fifteenth, however, would imply that it is but another in the long succession of revisions which only partially satisfied the demands created by constantly increasing knowledge. More truly descriptive is the name Standard Library Edition. In 1945 the pattern of the new revision was furnished by instructors in library schools and by librarians in a variety of libraries in North and South America and Great Britain. In accordance with their advice, the new edition is a complete revision, each schedule having been studied and rewritten in the light of new information, changing concepts and terminology, and Simplified spelling has been abandoned, except for the twelve words adopted by the N. E. A.

The revision is designed to meet the needs of the greatest number of libraries. As the ''greatest number" ranges from small to moderately large general libraries, the tables are evenly and broadly expanded. Overelaboration, which too often appeared in parts of previous editions, has been avoided. Numbers for which no book can be found have been omitted. To insure its fitness for classifying books in such libraries, each table has been scrutinized before its incorporation in this edition, not only by subject experts, but by librarians in public and university libraries of varying sizes.

In order that the reference value contained in the bibliographic fullness of some of the older editions may not be lost in less detailed expansions, liberal use has been made of definitions and scope notes in the Standard. So that its use may be simplified, definite recommendations are made when the possibility of alternative numbers arises. As reclassification is both a physical and financial impossibility for most libraries, no very drastic changes appear in the Standard. When it has seemed necessary for reasons of correction to use a number other than the original, the new classification is built upon a hitherto unused number. The old number is retained, but with the advice that use of the new classification is recommended.

Much unnecessary material has been omitted in the process of simplification. Punctuation has been reduced to a minimum; etc. has been omitted in confidence that the user will realize that no listings can possibly be complete. "May be divided like," except geographically, and other advice concerning subdivisions have been eliminated from almost all tables in the belief that the user does not need to be told how to arrange his collection.