Bretha Nemed Déidenach is the late title of an Early Irish law text dating from the eighth century.
The only surviving copy, now part of Trinity College, Dublin MS 1317 H.2.15B, was transcribed by Dubhaltach MacFhirbhisigh.
Bretha Nemed Déidenach contains extracts of works concerning poets and bards, along with passages on such subjects as fosterage, sureties, pledge-interests and land law.
Much of it is written in the alliterative rosc style in what is now called Archaic or Old Irish.
Another text in the same MS – Duil Laithne – was written at Ballymacegan, County Tipperary, on 5 May 1643, so the Déidenach may have been copied in that period.