Plethyn is a Welsh language folk music group that was at their zenith between 1978 and 1995. The members are Roy Griffiths, Linda Healy and John Gittins. The three members originate from Maldwyn, in mid-Wales. Roy and Linda are brother and sister; John Gittins was born on a neighbouring farm.
They specialise in the close harmonies of the "plygain" tradition. They have popularised a number of folk songs very much and created new songs in a traditional style. The principal influence on the group was Elfed Lewys.
Plethyn is also the Welsh word for "braid" or "bond".