There are two arrangements of the books in the library: everything cataloged until July 2006 is in an abbreviated Dewey Decimal classification, while everything cataloged after July 2006 is in the Library of Congress classification. The way to tell the difference is:

• • when a the classification starts with a number, e.g. 813.54 SIO, the number is a Dewey Decimal number
  • when the classification starts with a letter, e.g. HQ503.C66 2005, it is a Library of Congress number. For a map of the library and more information, see: Map of AUR Library.

• To find books in the AUR Collection, you must know how the bboks are arranged. For short discussions, see:
• How to Find Books in the Dewey Decimal Classification
• How to Find Books in the Library of Congress Classification
  

But, if you are going to use other collections, they very well may have different classifications from either of these. For example, the following book is held in several libraries in Rome:

La monarchia meridionale : istituzioni e dottrina giuridica dai Normanni ai Borboni / Mario Caravale. -- Roma : Laterza, 1998. -- 330 p. ; 21 cm. (Collana di fonti e studi ; 6) (Fonti e studi (Centro europeo di studi normanni) ; 6)

But the numbers that each library assigns is quite different:

This same book also has the following numbers:

If AUR would get this book today, we would assign the Library of Congress number.