El Cantar de mio Cid, literally "The Song of my Cid" (or El Poema de mio Cid), also known in English as The Poem of the Cid, is the oldest preserved Castilian epic poem (epopeya). Based on a true story, it tells of the Castilian hero El Cid, and takes place during the Reconquista, or reconquest of Spain from the Moors.
The Spanish medievalist Ramón Menéndez Pidal included the Cantar de Mio Cid in the popular tradition he termed the mester de juglaría. Mester de juglaría refers to the medieval tradition according to which popular poems were passed down from generation to generation, being changed in the process. These poems were meant to be performed in public by minstrels (or juglares), who each performed the traditional composition differently according to the performance context—sometimes adding their own twists to the epic poems they told, or abbreviating it according to the situation.
On the other hand, some critics (known as individualists) believe El Cantar de Mio Cid was composed by one Per Abbad (in English, Abbot Peter) who signed the only existing manuscript copy, and as such is an example of the learned poetry that was cultivated in the monasteries and other centers of erudition. Per Abbad puts the date 1207 after his name, but the existing copy forms part of a 14th-century codex in the Biblioteca Nacional de España (National Library) in Madrid, Spain. It is, however, incomplete, missing the first page and two others in the middle, and is written in Old Spanish.
Its current title is a 19th-century proposal by Ramón Menéndez Pidal; its original title is unknown. Some call it El Poema del Cid on the grounds that it is not a cantar but a poem made up of three cantares. The title has been translated into English as The Lay of the Cid and The Song of the Cid. Mio Cid is literally "My Cid", a term of endearment used by the narrator and by characters in the work. The word Cid originates from Arabic sidi or sayyid (سيد), an honorific title similar to English Sir (in the medieval, courtly sense).