The Edda, namely the Poetic Edda (Elder Edda/Sæmundar Edda) and Prose Edda (Younger Edda/Snorri's Edda), are collections of several Old Norse poems written during the 13th century in Icelandic, describing legends and myths reaching into the Viking Age. They are the main sources of medieval skaldic tradition in Iceland and Norse mythology.
Many are religious texts. The poems themselves from Poetic Edda were originally traditional minstrel poems that where later written down. The Prose Edda were written by Snorri Sturlasson in the 13th century, who preserved the the mythology of Scandinavia in Prose form. The Elder Edda was considered dangerous by Christians and were lost until rediscovered in 1643 on Iceland.