"Books" here refers to secondary scholarship about the medieval world, that is, books by scholars about the medieval world based on their knowledge and analyses of primary souces.
"Primary sources" are documents created by medieval people such as literary works, chronicles, or legal documents. Many primary sources have been printed in modern editions or translations. Others are unpublished archival materials. A growing number of these are becoming accessible in online formats, some in translation, others not.
"Sources" can be used in a subject search in InfoHawk/SmartSearch
The Internet Medieval Sourcebook based in the Fordham University Center for Medieval Studies is an extensive collection of links, not all of which may have been maintained or updated. The material is either in the public domain or used with permission.
Medieval Sources Online is a collection of documents in English translation..