Here is an example from one of these encyclopedias, looking at the SUBJECT INDEX for entries on COMPETITION (this is a two-page PDF).
In this case, if you only pulled the volume that carried entries starting with the letter "C", you would find less than 1/5th of all entries that actually discussed various aspects of Competition! Those other entries are scattered across sixteen of the volumes from this one encyclopedia!
The Mark O. Hatfield Library uses the Library of Congress classification system to group items with similar topics together. Each item is assigned a unique call number, which helps people to locate material on the shelf. The Library of Congress uses a combination of letters and numbers, and each call number begins with a letter.
To the right are the general call numbers and the main topics within the Library of Congress system. Click on any class to view an outline of its subclasses in an interactive PDF document.
This list is based off of the Library of Congress Classification Outline.
Below are key reference books that provide a general overview of a topic or help identify synonyms, related terms, or basic data. These sources often include references and lists of further readings.
The Blackwell Encyclopedia of Sociology by 
The Encyclopedia of Addictions and Addictive Behaviors by 
The Encyclopedia of Crime and Punishment by 
Encyclopedia of Drugs, Alcohol and Addictive Behavior by 
Encyclopedia of Public Health by 
Encyclopedia of Social Deviance by 
Encyclopedia of Social Networks by 
Encyclopedia of Social Problems by 
The Gale Encyclopedia of Prescription Drugs: a comprehensive guide to the most common medications by 
International Encyclopedia of the Social and Behavioral Sciences by 
Magill's Medical Guide by 
Mental Health Care Issues in America by 
The SAGE Encyclopedia of Economics and Society by 
Social Issues in America: an Encyclopedia by 
