Brother Cadfael is the main fictional character in a series of historical murder mysteries written between 1977 and 1994 by the linguist-scholar Edith Pargeter under the name Ellis Peters. The character of Cadfael himself is a Welsh Benedictine monk living at the Abbey Church of Saint Peter and Saint Paul, in Shrewsbury, western England, in the first half of the 12th century. The stories are set between about 1135 and about 1145, during "The Anarchy", the destructive contest for the crown of England between King Stephen and his cousin Empress Maud.

The historical mystery or historical whodunit is a subgenre of two literary genres, historical fiction and mystery fiction. These works are set in a time period considered historical from the author's perspective, and the central plot involves the solving of a mystery or crime. Though works combining these genres have existed since at least the early 20th century, many credit Ellis Peters's Cadfael Chronicles (1977–1994) for popularizing what would become known as the historical mystery. The increasing popularity and prevalence of this type of fiction in subsequent decades has spawned a distinct subgenre recognized by the publishing industry and libraries. Publishers Weekly noted in 2010 of the genre, "The past decade has seen an explosion in both quantity and quality. Never before have so many historical mysteries been published, by so many gifted writers, and covering such a wide range of times and places." Editor Keith Kahla concurs, "From a small group of writers with a very specialized audience, the historical mystery has become a critically acclaimed, award-winning genre with a toehold on the New York Times bestseller list."