Celebrated annually on 1st March, St David's Day (Dydd Gŵyl Dewi) marks the national day of Wales. It celebrates the life of Dewi Sant, or St David, the patron saint of Wales who is said to have died on this day in AD 589. The son of St Non, he was born in Pembrokeshire and grew up in Henfynyw, Ceredigion. As a child, St David healed his blind teacher, Paulinus, by placing his hands over the latter's eyes. One of Dewi Sant's most well-known miracles took place in Llanddewi Brefi, where he raised a mound of earth so that the gathered crowds could see and hear him better. As a lifelong vegetarian he did not consume meat or alcohol, only drinking water which gained him the nickname Dewi Dyfrwr ('Dewi the Waterdrinker'). He built a monastery at Glyn Rhosyn, which eventually developed into the cathedral and city of St Davids ('Tyddewi').

Today, St David's Day is celebrated in Wales and by Welsh people around the world by wearing the national costume, eating cawl and Welsh cakes, and parades. In schools and other groups, eisteddfodau are also held and songs sung. Another important part of the day is to 'Do the little things' ('Gwnewch y pethau bychain'), the advice St David gave in one of his last sermons.