Primary sources are firsthand accounts of an event -- or original records created during that time period -- which do not contain any outside interpretation. Primary sources can include letters, diaries, or interviews; historical news reportage; original works of fiction, art, or music; testimony or speeches.
When and Why You Should Use Primary Sources:
Remember: Primary sources are the building blocks of historical research and should provide the foundation of your argument and interpretation, whereas secondary sources should inform and supplement the primary sources. Use your primary sources as evidence for answering your research question and write based on those sources, rather than “plugging them in” after the fact to bolster your argument. In short, primary sources should drive the paper, not the other way around.
Newspapers and periodicals are useful because they can contain original reviews of works as well as earlier, serialized versions of works which may offer textual variations. Newspapers also provide accounts of what was occurring when the work was published. Ultimately, newspapers are invaluable for their immediacy, recording history as it happened.
Ephemera is useful because its sheer variety (posters, maps, advertisements, trade cards, programs, etc.) provides a glimpse into a historical period's cultural, economic, and social customs & traditions.