[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.

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.

Ya sennor glorioso, padre que en çielo estas, Fezist çielo e tierra, el terçero el mar, Fezist estrelas e luna, e el sol pora escalentar, Prisist encarnaçion en Sancta Maria Madre, En Belleem apareçist, commo fue tu veluntad, Pastores te glorificaron, ovieronte a laudare, Tres Reyes de Arabia te vinieron adorar, Melchior e Gaspar e Baltasar, oro e tus e mirra Te offreçieron, commo fue tu veluntad.

Saluest a Jonas quando cayo en la mar, Saluest a Daniel con los leones en la mala carçel, Saluest dentro en Roma al sennor San Sabastián, Saluest a Sancta Susanna del falso criminal, Por tierra andidiste XXXII annos, sennor spirital, Mostrando los miraclos, por èn auemos que fablar, Del agua fezist vino e dela piedra pan, Resuçitest a Lazaro, ca fue tu voluntad, Alos judios te dexeste prender, do dizen Monte Caluarie Pusieronte en cruz, por nombre en Golgota, Dos ladrones contigo, estos de sennas partes, El vno es en parayso, ca el otro non entro ala, Estando en la cruz vertud fezist muy grant, Longinos era çiego, que nuquas vio alguandre, Diot con la lança enel costado, dont yxio la sangre, Corrio la sangre por el astil ayuso, las manos se ouo de vntar, Alçolas arriba, legolas a la faz, Abrio sos oios, cato atodas partes, En ti crouo al ora, por end es saluo de mal.

En el monumento Resuçitest e fust alos ynfiernos, Commo fue tu veluntad, Quebranteste las puertas e saqueste los padres sanctos.

Salvaste a Jonás cuando cayó en el mar, Salvaste a Daniel con los leones en la mala cárcel, Salvaste dentro de Roma al señor San Sebastián, Salvaste a Santa Susana del falso criminal, Por tierra anduviste treinta y dos años, Señor espiritual, Mostrando los milagros, por ende tenemos qué hablar, Del agua hiciste vino y de la piedra pan, Resucitaste a Lázaro, porque fue tu voluntad, Por los judíos te dejaste prender, donde llaman Monte Calvario Te pusieron en la cruz, en un lugar llamado Golgotá, Dos ladrones contigo, estos de sendas partes, Uno está en el paraíso, porque el otro no entró allá, Estando en la cruz hiciste una virtud muy grande, Longinos era ciego que jamás se vio, Te dio con la lanza en el costado, de donde salió la sangre, Corrió la sangre por el astil abajo, las manos se tuvo que untar, Alzándolas arriba, llevándolas a la cara, Abrió sus ojos, miró a todas partes, En ti creyó entonces, por ende se salvó del mal.