Primary literature refers to sources of original information. Often providing first hand accounts of the author's own work, primary literature typically presents the most recent research or scholarly discussion on a given subject and can often refer to methodology and particular results.
A common place to find primary literature would be journal articles. Journals (or periodicals) are continuous publications, usually published at regular intervals. Peer-reviewed or refereed journal articles have been evaluated by subject experts prior to publishing.
Internet resources such as websites for professional associations, conferences and academics' personal web pages may also provide access to primary literature. Internet resources should always be carefully evaluated.
Secondary literature is normally a synthesis or overview of theories or research. Edited books or textbooks are examples of secondary literature.
Review articles and review journals are a common and popular secondary source also. These articles normally summarise the latest range of research on a certain topic or contentious issue. They are usually written by an expert in the field and contain an extensive list of references.