Chasca, Edmund de. The Poem of the Cid. Boston: Twayne, 1976. The best place to begin for a general literary and historical account of the poem. Includes a discussion of medieval epic poetry, the historicity of Poem of the Cid, use of humor, epic formulas, and speculation on authorship.
Fletcher, Richard A. The Quest for the Cid. New York: Random House, 1990. A historical account of the period 711-1516, providing a valuable discussion of the cultural background to El Cid. Also contains an extensive bibliography.
Matulka, Barbara. The Cid as a Courtly Hero. New York: Columbia University, Institute of French Studies, 1928. Explores the figure of the Cid from his appearance in medieval epic through Corneille’s treatment in The Cid (1636). Short, useful account of such literary motifs as the love-test, voluntary death, and the Cid’s sword.
Menéndez Pidal, Ramón. The Cid and His Spain. Translated by Harold Sunderland. London: John Murray, 1934. A detailed discussion of El Cid and its background by the author of the poem’s most influential critical edition. Includes attention to the struggle for Valencia, the invasion (and subsequent repulsion) of the Almoravides, the court of the Cid, and the process by which the historical figure of the Cid was transformed into a legend.
Smith, Colin. The Making of the “Poema de mío Cid.” Cambridge, England: Cambridge University Press, 1983. Claims that Poem of the Cid was an experimental work, the first epic to be composed in Castilian, and that Per Abad, the figure who is usually regarded as the poem’s copyist, was actually its author.