Held on the 19th May. St Yves' Day is named after one of the patron saints of Brittany: Saint Yves, the "Advocate of the Poor" who is also the patron saint of lawyers and abandoned children.

The modern observance of St Yves as a national symbol of Brittany started in the late 20th century when Celtic Revivalists sought to provide the people of Brittany with a national day similar to those observed in other nations. Since 2001 the celebration has become increasingly observed thanks to the support of Région Bretagne, Brittany's devolved government.