Codex Regius or GKS 2365 4º is an Icelandic codex in which many Old Norse poems from the Poetic Edda are preserved. Thought to have been written during the 1270s, it is made up of 45 vellum leaves. The work originally contained a further eight leaves, which are now missing. It is the sole source for most of the poems it contains. In scholarly texts, this manuscript is commonly abbreviated as [R] for Codex Regius, or as [K] for Konungsbók.

Old Norse, Old Nordic, or Old Scandinavian is a stage of development of North Germanic dialects before their final divergence into separate Nordic languages. Old Norse was spoken by inhabitants of Scandinavia and their overseas settlements and chronologically coincides with the Viking Age, the Christianization of Scandinavia and the consolidation of Scandinavian kingdoms from about the 8th to the 15th centuries.