Primary sources are items closest to the original firsthand accounts of an event. This includes sources such as diaries, artifacts, or newspaper articles written at that time. Primary sources can come in multiple formats, including photographs, recorded videos or audio, as well. Original works are also considered primary sources, such as art, poems, films, and other literary works.
Secondary sources are those that were created in relation to the primary resource that originated elsewhere. This type of source includes analyses and interpretations that you might see in textbooks, reference works, commentaries, and articles.
A tertiary source is one that has compiled both primary and secondary works in one place, such as an entire textbook, reference source, dictionary, database, or journal.
Examples by Discipline
| Primary sources | Secondary sources | Tertiary sources |
| Diaries Interviews Letters Original works of art Photographs Speeches Works of literature |
Biographies Dissertations Indexes, abstracts, bibliographies (used to locate a secondary source) Journal articles Monographs |
Dictionaries Encyclopedias Handbooks |
| A primary source is an original document containing firsthand information about a topic. Different fields of study may use different types of primary sources. | A secondary source contains commentary on or discussion about a primary source. The most important feature of secondary sources is that they offer an interpretation of information gathered from primary sources. | A tertiary source presents summaries or condensed versions of materials, usually with references back to the primary and/or secondary sources. They can be a good place to look up facts or get a general overview of a subject, but they rarely contain original material. |
Examples:
| Subject | Primary | Secondary | Tertiary |
| Art | Painting | Critical Review of Painting | Encyclopedia entry on the artist |
| History | Civil War Diary | Book on Civil War battle | List of battle sites |
| Literature | Novel or poem | Essay about themes in the work | Dictionary of literary terms |
| Political Science | The Geneva Convention | Article about prisoners of war | Chronology of treaties |
(Adapted from: VirginaTech Library and University of Kentucky under Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License.)
| Primary sources | Secondary sources | Tertiary sources |
| Conference proceedings Interviews Journals Lab notebooks Patents Preprints Technical reports Theses and dissertations |
Monographs Reviews Textbooks Treatises |
Compilations Dictionaries Encyclopedias Handbooks Tables |
| These are where the results of original research are usually first published in the sciences. This makes them the best source of information on cutting edge topics. However the new ideas presented may not be fully refined or validated yet. | These tend to summarize the existing state of knowledge in a field at the time of publication. Secondary sources are good to find comparisons of different ideas and theories and to see how they may have changed over time. |
These types of sources present condensed material, generally with references back to the primary and/or secondary literature. They can be a good place to look up data or to get an overview of a subject, but they rarely contain original material. |
Examples:
| Subject | Primary | Secondary | Tertiary |
| Agriculture | Conference paper on tobacco genetics | Review article on the current state of tobacco research | Encyclopedia article on tobacco |
| Chemistry | Chemical patent | Book on chemical reactions | Table of related reactions |
| Physics | Einstein's diary | Biography of Einstein | Dictionary of relativity |
(Adapted from: VirginaTech Library and University of Kentucky under Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License.)