The Encyclopedia of Associations gives information about specific associations and divides them into different types:
There are print versions of both the Encyclopedia of Associations (American organizations) and The Encyclopedia of Associations (international organizations) located in the Reference Collection on the 1st floor of Hale. More recent editions are available electronically.
Institutional websites often contain rich and detailed information about the purpose and mission of the association. In a search engine, try searching for a particular association or keywords related to associations that interest you. For example, if you're interested in dental associations try searching for something like:
"American Dental Association" or "dental associations"
In many popular and some scholarly articles, journalists often quote institutions as reputable sources. If you read an article that quotes an association you're not familiar with, try finding out more information about them by using a search engine or the sources available at the library.