Côtes-d'Armor (French pronunciation: [kot.daʁ.mɔʁ]; Breton: Aodoù-an-Arvor) is a department in the north of Brittany, in northwestern France.

Côtes-du-Nord was one of the original 83 departments created during the French Revolution on 4 March 1790. It was created from part of the former province of Brittany. Its name was changed in 1990 to Côtes-d'Armor (ar mor meaning the sea in Breton). The name also has a historical connotation recalling the Roman province of Armorica.

The present department corresponds to most of historical Trégor, part of Cornouaille, and most of Saint-Brieuc.

Côtes-d'Armor is part of the current administrative region of Brittany and is surrounded by the departments of Finistère, Morbihan, and Ille-et-Vilaine, with the English Channel to the north.

The inhabitants of the department are called Costarmoricains.

The Côtes-d'Armor has usually been a left-wing holdout in a historically strongly clerical and right-wing Brittany, due to the department's more anti-clerical nature, especially in the inland area around Guingamp, a former Communist stronghold.

Armour or armor (see spelling differences) is protective covering used to prevent damage from being inflicted to an object, individual or a vehicle through use of direct contact weapons or projectiles, usually during combat, or from damage caused by a potentially dangerous environment or action (e.g., cycling, construction sites, etc.). Personal armour is used to protect soldiers, and war animals such as war horses (the application for the latter called barding). Vehicle armour is used on warships and armoured fighting vehicles.

The word "armor" was introduced into use in the Middle Ages as a borrowing from the French. It is dated from 1297, as a "mail, defensive covering worn in combat" from Old French armoire, itself derived from the Latin armatura "arms and/or equipment" with the root arma "arms or gear".

Armour has been used throughout recorded history. It has been made from a variety of materials; from rudimentary leather protection, personal armour evolved to Mail and full plated suits of armor. For much of military history the manufacture of metal armour in Europe has dominated the technology and employment of armour. Armour drove the development of many important technologies of the Ancient World, including wood lamination, mining, metal refining, vehicle manufacture, leather processing, and later decorative metal working. Its production was influential in the industrial revolution, and influenced commercial development of metallurgy and engineering. Armour was the single most influential factor in the development of firearms that revolutionised warfare.