The design and customs associated with it originated in the Irish fishing village of Claddagh, located just outside the old city walls of Galway, now part of Galway City. The ring, as currently known, was first produced in the 17th century, but the name Claddagh ring was not used before the 1830s. In recent years it has been embellished with interlace designs and combined with other Celtic and Irish symbols.
The ring belongs to a group of European finger rings called "fede rings". The name "fede" derives from the Italian phrase mani in fede ("hands [joined] in faith" or "hands [joined] in loyalty"). These rings date from Roman times, when the gesture of clasped hands was a symbol of pledging vows, and they were used as engagement/wedding rings in medieval and Renaissance Europe.
Incidentally, "Top of the morning to you." "And the rest of the day to yourself." Both are Hollywood inventions and never used in Ireland.