Lanvallay (French pronunciation: [lɑ̃valɛ]; Breton: Lanvalae) is a commune in the Côtes-d'Armor department of Brittany in northwestern France. In 1973 it absorbed two former communes: Tressaint and Saint-Solen.

Inhabitants of Lanvallay are called côtissois in French.

There is a twinning arrangement with Walkern, Hertfordshire. This was initiated around the time of the 800th anniversary of the Magna Carta.