At its core, Richard Fletcher's The Quest for El Cid is a key piece of historical revision in our understanding of the Spanish Middle Ages. In his book, he takes a scholarly approach to understanding a figure—Rodrigo Diaz de Vivar—who has been mythologized into a symbol of Spanish national identity.

Fletcher discovers along the way that some aspects of El Cid's life can be traced to historical fact, but many others have been embellished as part of Spanish lore. In doing so, Fletcher challenges previously accepted history about the eleventh century, and paints a knowledgable and complex portrait of life on the Iberian peninsula during a time of highly factionalized strife and sectarian conflict.

El Cid was a nobleman and military leader in medieval Spain, during a time when the Iberian peninsula was divided between warring nation-states and private military factions, and wracked by the increasingly religious war between Christians and Muslims, known in Spain as the Reconquista. Over his lifetime, he served and was exiled by various kings, and eventually led his own army in battles against various nation-states and other powers, coming, by the end of his life, to rule an independent principality, Valencia, on the coast of Spain.

A major purpose of Fletcher's book is to disentangle the facts of El Cid's life and the circumstances of Spain during his lifetime from the many works of fiction and art that were written about him after his death. El Cid has become a major symbol of Spanish chivalry and a hero of the Reconquista, in part because of several epic poems, many plays, and even a move, starring Charlton Heston, about his life. Fletcher tackles the reality of El Cid as a person living in history: we really don't know very much about him, but we can do our best to understand his place in the time that he lived.