While it has often been said, "information is power," ask a person that has misplaced a source if they still feel powerful. No, information does no one any good unless it can be retrieved when needed in a timely, economical basis. 

The goal of a librarian is not just to accumulate resources and information - professional librarians enhance the value of library collections by providing for "intellectual access" that allows users to locate information they need regardless of their depth of understanding of a given topic.
Libraries achieve this through the way they classify and catalog information. 

Simply stated, classification assigns a number to an item so that it can be shelved or grouped together with related or similar items. Cataloging is a procedure that describes an item with details such as title, author, publisher, date, physical description, subject headings, and edition. Classification

According to Arthur Maltby's Manual for Classification for Librarians, library classification is the art of arranging by subject "books and other materials on shelves or of catalogue and index entries in the manner which is most useful to those who read or who seek a definite piece of information."

Libraries enhance the value of their collections by presenting resources in a logical order and in convenient to browse shelves. This makes it easy to locate items that will fill a patron's information needs.

Cataloging

Of course this classification is helpful, but spatial arrangements are not enough. Libraries also need a systematic index that allow users to quickly and easily search through a collection to determine what resources are available to meet a specific information need and then locate them on the shelves. 

Together, these 2 factors provide the starting point for building intellectual access. The process starts by:

1. Identifying the subject(s) in a particular resource.
2. Applying subject headings that reflect the topics within that resource.
3. Applying the classification system which dictates what items are shelved together and where those resources are placed in the library.

The purpose of subject headings is to allow library users to find useful items without knowing titles or authors. K-12 school libraries use the Dewey Decimal System, which assembles like resources together on shelves that facilitate browsing. The customer may also browse through the library catalog to locate where useful resources are regardless of how the items are physically classified. 

Many small libraries start with "Level One" cataloging which includes the title, author, edition, publisher, date, physical description of the book, notes, standard number, Dewey number, and subject headings. Other information is added to reflect the information needs and usage patterns of the community. The Library of Congress maintains "full cataloging" which represents comprehensive information on over 12 million resources.