One of the first challenges posed by a historical research project is discovering primary sources that will reveal what it is a researcher wants to find out. That involves some previous knowledge of the kinds of sources available and questions about how those sources were produced, who produced them, and for what reasons. Those questions can be difficult to answer. But one way of approaching the problem is to break the issue down into three different categories: (a) the nature of the source; (b) the persons or institutions responsible for the production of the source; and (c) what makes that source historically significant—in other words, why it matters to the subject under investigation.