•Primary:       original information;  eg. correspondence, diaries, research.
•Secondary:  interprets primary information, eg. scholarly journals, books. This is where research is reported.
•Tertiary:      interprets secondary information, eg. reference books, encyclopedias
Use for background information
 
•Reference sources: overview of topic eg. encyclopedias, in print or electronic.
•Books:                     analysis of topic, in depth background information.
•Journal articles:       focus on specific subject.
•Grey literature:        governments, organizations, think tanks – not publishers.
•Web pages:             eg. government webpages such as gov.za.