Here we present a translation into Spanish of the medieval English poem titled “Sir Orfeo”, which was composed in the late 13th or early 14th centuries within the WestminsterMiddlesex area. Our main spur has been to disseminate it amongst the modern Spanish-speaking readers due to its literary beauty and its story, a story which is not certainly innovative; however, it is innovative as to the way its author has succeeded in adapting the classical or Ancient Greek myth to the medieval English mindset of the readers or listeners of the time so as to arouse their interest, entertain them and teach them with a didactic purpose. The poem comprises all the elements inherent to a prototypical lay (or lai): a knight-king, a love story, a physical and spiritual quest, the otherworld (or fairyland), and moral and spiritual values which should be taken into account by the audience. We have attempted to make the translation of “Sir Orfeo” into Spanish as faithful as possible regarding the original English poem in order to maintain its literary essence, freshness and character. “Sir Orfeo” was a very popular poem in its time, and there is no doubt that it will become popular again in the 21st century in the light of different perceptions and approaches.