Secondary sources are the published work of scholars specializing in the topic. Secondary sources include scholarly books, articles, and essays (both analyses by contemporary scholars as well as older analyses), surveys, criticism, comparative studies, reference sources, and works on theory and methodology; this is also termed the secondary literature. Eventually you will need to decide which interpretation makes the most sense to you and seems consistent with your primary sources, or if you wish to offer a new interpretation. 

When we talk about secondary sources, most of the time we are referring to published scholarship on a subject, rather than supplemental material (bibliographies, encyclopedias, handbooks, etc.). Secondary literature is published in both book form and as articles in periodicals, either in print or digital format. (Digital format includes both reproduction of print material online and original e-text.) This scholarship is analytical and interpretive. It may synthesize the work of other historians to present a totally new interpretation. More likely, it offers a new reading of previously analyzed sources or presents an analysis of previously unknown sources.

Hence, you use secondary sources to identify the main currents of thought on your topic. Which historians have taken up this topic and what were their main arguments? How has our understanding of the subject changed with shifts in the predominant methodologies and theoretical perspectives in the historical profession?

Primary sources are produced at the time of the event or phenomenon you are investigating, and they purport to document it. They reflect what someone observed or believed about an event at the time it occurred or soon afterwards. These sources provide raw material that you will analyze and interpret. Primary sources can be published or unpublished. 

There are different types of primary sources for different historical periods. For example, church documents and saints' lives serve as primary sources for the study of medieval history, while newspapers, government reports, and photographs serve as primary sources for the modern period. Moreover, what constitutes a primary source depends in part on how you have formulated your research topic. An article in an academic journal from 1984 could be a secondary source because it is part of an ongoing scholarly analysis of your topic, or it could be primary source because it provides evidence of attitudes and opinions held by people in 1984. In other words, there is no intrinsic or distinguishing feature of a text that makes it a primary, rather than a secondary, source. In fact, many sources, whether visual or textual, can serve as either primary or secondary sources. The key is how you use the material. In order to determine whether a source might be primary or secondary for your purposes, you must consider it in relation to your particular topic.

Unpublished primary sources are original documents and artifacts of all kinds that were created by individuals but not published (that is, made public --issued in a format that could be widely distributed) during the period you are studying. In the past, only archives and museums preserved these kinds of primary source materials, and researchers had to travel all over the world to use them. With the invention of microfilming, and later, digitization, it became possible to create facsimiles of large collections of primary source materials. Large research libraries like the UIUC Library have extensive collections of microfilm and digital facsimiles of unpublished primary sources. Universities also have rare books libraries and university archives, which hold original unpublished primary source materials.

In general, published primary source material covers a wide range of publications, including first-person accounts, memoirs, diaries, letters, newspapers, statistical reports, government documents, court records, reports of associations, organizations and institutions, treatises and polemical writings, chronicles, saints' lives, charters, legal codes, maps, graphic material (e.g. photographs, posters, advertising images, paintings, prints, and illustrations), literary works and motion pictures. Some of these materials were not published at the time of their creation (e.g. letters), but have subsequently been published in a book. For example, The Selected Papers of Margaret Sanger is a selection from birth control activist Margaret Sanger's letters and other unpublished papers, presented in chronological order, which contextual information provided by expert editors.

Here's an overview:

There are many ways to find digitized primary sources, both published and unpublished, starting with our Digital Collections guide:

You can find published primary sources by using library catalogs, research guides, and published bibliographies. You can also look at secondary literature on your topic to ascertain what sources other scholars have used in their research. Our Guide to Primary Source Reprints is another good place to look for published primary sources:

To find published primary sources in library catalogs, try these strategies:

-Search by date of publication to find sources that were published during the time period you're researching --you can also use this strategy in full-text digital collections such as ProQuest Historical Newspapers

-Use the library catalog advanced search option and include one or more of these Library of Congress Subject Heading form subdivisions as subject search terms:

• Correspondence
• Sources
• Diaries
• Personal narratives
• Interviews
• Speeches
• Documents
• Archives
• Early works to 1800
• Manuscripts

You can find unpublished primary sources in the University of Illinois Library in the library catalog and in the University Archives Holdings Database. You can find materials held by other archives and museums using ArchiveGrid (an inventory of archival finding aids), or using the "archival material" format in WorldCat. Microfilm facsimiles of primary source materials are also included in WorldCat and other library catalogs: