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TC Library Online

A guide to library resources

Introduction to Types of Sources

Sources can be defined at least two different ways. When people use the phrase "types of sources" they may be referring to the:

  1. Level or distance from the original source of information (primary, secondary, tertiary)
  2. Format of the information source (book, article, movie, blog, etc.)

This guide will clarify both types of definitions. Which source is the best? It depends! Each source has unique characteristics which need to be considered when making the decision to use a source for research.


Information sources are usually organized by type; however, the level of a source is important to understand.

Primary sources are first hand accounts of an event. For example, a book of poems, a photograph, an autobiography, an interview are all primary sources.

Secondary sources are one step away from the primary source. For example, a review of a book of poems, a book with copies of the original photographs, a biography about a person are all secondary sources.

Tertiary sources are at least two steps away from the primary source. For example, an encyclopedia of 17th century poets, a catalog of photographs used in an exhibit, a review of biography of a person.


A source may be in print, printed online, such as a webpage or on a device, an audio recording, such as a CD or DVD, or other types of physical format. Additionally, sources are also available electronically such as an e-Book.