Secondary sources are written by scholars who didn't experience the events they are writing about. They can include books, articles, and documentary films.
Secondary sources use primary sources as data to construct a description of events or support a thesis about them.
In History, most scholarly communication takes place in the form of books, because so much information has to be passed along. Articles also are used but are less prevalent than in scientific and technical fields.
* Annales School
The foundations of modern historical scholarship, the Annales school was founded in the 20th century. It focuses on long-term social history and a close reading of primary sources. Focuses include the study of beliefs and mentalities and the connections between culture and society.
* Revisionist History
The most recent historical thinking is often revisionist: challenging and sometimes clashing with accepted versions of events. Revisionism often brings marginalized cultures, women's history, and LGBTQ history into focus. Revisionist history is extremely valuable but can sometimes fall prey to presentism or become overly concerned with modern politics.
Other areas to know about: economic history, history of ideas, history of science, ethnohistory, and archeological theory.
Who is the author? Is he or she an expert in the field? If a book was published by a university press, that's a good sign.
Helpful Hint: Be careful with documentaries from channels where every other show is about space aliens.
When was the book written? Historical scholarship ages slowly. In most cases a book won't be outdated for decades. Still, eventually it does happen!
Does the resource use primary sources effectively throughout?
Are the arguments logical?
Is the material relevant to your content?
Helpful Hint: Let your research tell you what to write about. Don't decide what you want to say and cherry-pick quotes to support it.