No code can take the place of discrimination, sound judgment, and knowledge of the field of rare books. There are, however, certain general criteria, which all should know and apply when fitting. Simply stated, rare books are uncommon books. More specifically, rare books are identified by their contents or physical characteristics which command more than ordinary attention among book collectors, librarians, scholars and booksellers. When, however, a book possessing either or both of these qualities contains additional significant features which make it both unusual and of great interest, then it may be considered valuable.
Many qualities can make a book unusual and interesting.
A beautiful or peculiar binding, typographical excellence and illustrations by a noted engraver are a few of the external characteristics which influence value. Previous ownership by a distinguished person frequently lends luster to an otherwise prosaic volume. But the contents of a book and the esteem with which it is regarded are controlling factors in determining whether or not a book is properly considered a rarity.