[2] Based on a true story, it tells of the deeds of the Castilian hero and knight in medieval Spain Rodrigo Díaz de Vivar—known as El Cid—and takes place during the eleventh century, an era of conflicts in the Iberian Peninsula between the Kingdom of Castile and various Taifa principalities of Al-Andalus.

For example, the poem ends with a request for wine for the person who has recited it (Es leido, dadnos del vino).

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[4]) who appears to be credited as the writer of the work in a colophon to the text.

However, Per Abbad puts the date 1207 after his name and current thinking is that his claim to have written the work has simply been copied along with the text of an earlier manuscript now lost.

The existing copy forms part of a 14th-century codex in the Biblioteca Nacional de España (National Library) in Madrid, Spain.

[5] These, however, recognize that the poem itself would not have been written immediately after the death of its titular hero since the narrative would not have been picked up if the story of the Cid had not yet attained its legendary status.

[6] One of the oldest documents preserved at the Real Academia de la Historia in Madrid presents only this phrase as the poem's title: Hic incipiunt gesta Roderici Campi Docti, which means "Here begin the deeds of Rodrigo the Campeador.

[4] The word Cid originates from Arabic sidi or sayyid (سيد), an honorific title similar to English Sir (in the medieval, courtly sense).

El Cid defends the city of Valencia, defeating King Chufa ibn Tashfin of the Almoravids.

It is discovered that the Infantes (princes) de Carrión, the nephews to the king, are the enemies who caused Cid's exile.

The infantes of Carrión were put to shame after being scared of a lion roaming in the court and running away from a campaign to fight against the Moors.

Once on the journey, they send the escort ahead of them, steal their wives' great dowries (including two beautiful swords) and beat them and leave them for dead.

In the middle of the trial, a message is sent from the kings of Navarra and Aragon, proposing to marry their sons to Cid's daughters.

[9] Certain aspects of the conserved text belong to a well-informed author, with precise knowledge of the law in effect by the end of the 12th century and beginning of the 13th, who knew the area bordering with Burgos.

[10] The format has been somewhat regularized (e.g., "mio" for "myo", "rr" for "R", "ñ" for "nn", "llorando" for "lorando", "v" for "u", adding modern punctuation and capitalization): (The last verse is not in the original transcript by Per Abbat, but it was inserted by Menéndez Pidal because it appears in later chronicles, e.g., "Veinte Reyes de Castilla (1344)".

[11]) The following is a sample from Cantar de Mio Cid (lines 330–365), with abbreviations resolved, punctuation (the original has none), and some modernized letters.