A primary resource is information that originates directly from the source created at the time historical events occurred or well after events in the form of memoirs or oral histories. Examples include laws issued by Congress, annual reports of businesses, autobiographies, text of interviews, and newspaper articles reporting current events.

A secondary resource is a work that attempts to interpret or analyze a subject. Examples include biographies and journal articles.

A fee-based Internet subscriptionis a database that is available only to paid subscribers. These searchable databases are intended to provide information on a specific topic or type of resource. PAIS International is an example of a fee-based subscription.

A free Internet site can provide a wide range of information types, but must be used with care. Always evaluate the quality of the information provided including obvious bias, blatant inaccuracies and a stale posting date.

A scholarly resource is the in-depth treatment of a specific topic and is often sponsored by an academic or research institution, the author's credentials are clearly stated, and the text is verified and supported with extensive footnotes and bibliographies.

A popular resource is a general treatment of a subject written by a reliable source, usually a staff member of a commercial publishing company. Some reference to sources used may be mentioned in the body of the article, but popular materials rarely include footnotes.