Special collections are libraries or departments within libraries that store, protect, and provide access to rare and/or unique books, and other materials that do not normally fall within the scope of a library’s circulating collections.
Materials in these collections are kept in a separate department because of the need for special handling, for security, and sometimes because of their monetary value or their rarity. The definition of rarity is tricky and can differ according to book collectors and to rare book librarians, as each may have different goals in building their collections.
Some books are considered rare because of:
Example: A good example of a universally acknowledged rare book is the Gutenberg Bible. This Bible is considered to be the first book that was printed with movable type. There were only 180 copies of this Bible printed, and currently less than 50 survive. Of these 50 existing copies only 21 are complete.