Mudiad Amddiffyn Cymru

Mudiad Amddiffyn Cymru (Movement for the Defence of Wales) was a Welsh Nationalist group that committed arson attacks in the early sixties.

The group's origins were in protests against the 1963 flooding of a Welsh village to create the Tryweryn reservoir to provide water for Liverpool. The group was reformed in 1967 by leader John Jenkins, this time protesting the investiture of the Prince of Wales with an organised bombing campaign.

The group planned to launch a bomb attack on the day of the investiture, 1 July 1969, apparently targeting the railway on which the royal train would be traveling. The plan went badly wrong and the bomb detonated at some council offices in Abergele, killing two men. The victims, Alwyn Jones and George Taylor, were generally assumed to have been planting the bomb, although Taylor's daughter has argued that her father may have been trying to prevent the attack.

The group also planted a bomb at Llandudno pier in an attempt to prevent Royal Yacht Britannia from docking, although it did not go off.

Jenkins was arrested in 1969 and the group was dissolved. Welsh nationalism would return for more arson in the 1980s with Meibion Glyndŵr (sons of Glyndŵr), who burned down English-owned holiday homes when the overflow of holiday homes affected house prices. Only one member of the latter group was ever caught and it has had a far more lasting effect than MAC.