The main purpose of this article is to introduce the modern reader into the medieval English poem Sir Orfeo as to its origins, authorship, extant manuscripts, argument, characters, its relationship with the classical Greek myth of Orpheus and its relationship with the Celtic folklore in reference to the Otherworld. The approach of the article is eminently exploratory, descriptive, and informative, and is spurred, therefore, by the need to contextualize the medieval English poem from the historical and literary viewpoint before the reader carries out its preliminary reading. The introduction, therefore, will offer a general internal and external outlook of the English poem, and will briefly compare the interpersonal relationship between Orpheus and Eurydice as characters and the intrapersonal relationship between Orpheus and Eurydice with the Greek Underworld with this same interaction established between Orpheus and Heurodis as characters and Orpheus and Heurodis with the Celtic-style Otherworld of the English poem. The article includes, in addition, a fragment of the original poem in Middle English and its translation into modern Spanish which may provide readers with an idea of the classical Breton lay structure in Middle English, based upon Marie de France’s lays, an author who contributed decisively to fostering this kind of poems in Henry II’s England, and encourage other authors to continue in this line. Such lays could combine courtly love with the Supernatural World through appealing characters, such as knights, noble ladies, supernatural beings and, in some cases, mythological creatures.