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 Gittings. Roy and Linda are brother and sister, with John Gittins born on a farm, near Meifod in Maldwyn.
Their style shows influence of the plygain singing of this area: simple, close harmony. 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".