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Primary, Secondary, Tertiary Sources: Guide


This research guide contains information about primary, secondary, and tertiary sources. If you get stuck, please ask a librarian!

Primary sources offer firsthand evidence. In the humanities, this might be letters, diaries, or creative works. In the sciences, the article that first reports the results of an experiment or trial is considered a primary source.  

Secondary sources are one step removed from the primary source. They analyze or interpret past events, creative works, or research findings.

Tertiary sources are "sources about sources" - several steps removed from the primary source. Their focus is on presenting information that is widely agreed on. They are sometimes published with no named author. Examples are general encyclopedias and bibliographies. 

Primary, Secondary and Tertiary Source Definitions

Primary sources online

In addition to looking at the websites highlighted below, try searching the Web for your topic combined with a word like News, Photos, Interviews, Journals, or Primary Sources. For example, by searching the Web for:

Selena Quintanilla-Pérez primary sources

We can find a video recording housed in the Portal to Texas History and a description of physical items housed at the Whitliff Collections at Texas State University

Primary sources in the TLU library

Library Catalog

You can find primary sources in the TLU Library by searching the library catalog. Use Advanced Search to combine your search term with the subject heading Sources (use the drop-down menu to select Subject). 

Reader's Guide to Periodical Literature

The library has an index called the Reader's Guide to Periodical Literature. It is a physical reference source located on the main floor. You can use it to find articles by subject in the library's bound periodicals such as:

  • Time (starting in 1927)
  • Harper's Monthly Magazine (starting in 1902)
  • The Atlantic (starting in 1981)
  • Good Housekeeping (starting in 1930)

You can also use the Reader's Guide to locate periodical articles that the library does not own and request them through ILL. 

Guide Editor

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Amelia Koford
Library Office 115

Ask a Librarian

Reference desk

TLU librarians offer in-depth research help.


During library open hours, ask at the main desk for help finding what you need or help setting up an appointment with a librarian. 



Click on the Ask a Question tab on the right side of a library web page. It will bring you either to live chat, or to a place where you can leave a message. 


830-372-8100 (main desk)

Library directory (list of individual library staff and faculty)



--Interlibrary Loan--

Need an item that our library doesn't own? No worries, you can email the title, author and date of what you need to or fill out a form. We can get most (but not all) articles within 2 days and many books within 4-8 days. 

For more information, visit our interlibrary loan page.