A military or an armed force is a professional organization formally authorized by a sovereign state to use lethal or deadly force and weapons to support the interests of the state. It typically consists of branches such as an Army, Navy, Air Force, and in certain countries, Marines and a Coast Guard. The task of the military is usually defined as defence of the state and of its citizens, and as the prosecution of war against other states. The military may also have additional sanctioned and non-sanctioned functions within a society, including, the promotion of a political agenda, protecting corporate economic interests, internal population control, construction, emergency services, social ceremonies, and guarding important areas. The military may also function as a discrete subculture within a larger civil society, through the development of separate infrastructures, which may include housing, schools, utilities, logistics, health and medical, law, food production, finance and banking.
In broad usage, the terms "armed forces" and "military" are often treated as synonymous, although in technical usage a distinction is sometimes made in which a country's armed forces may include both its military and other paramilitary forces. Armed force is the use of armed forces to achieve political objectives. There are various forms of irregular military forces, not belonging to a recognized state; though they share many attributes with regular military forces, they are less often referred as simply "military".

The profession of soldiering as part of a military is older than recorded history itself. Some of the most enduring images of classical antiquity portray the power and feats of its military leaders. The Battle of Kadesh in 1274 BC was one of the defining points of Pharaoh Ramses II's reign, and his monuments commemorate it in bas-relief. A thousand years later, the first emperor of unified China, Qin Shi Huang, was so determined to impress the gods with his military might that he had himself buried with an army of terracotta soldiers.
The Romans paid considerable attention to military matters, leaving to posterity many treatises and writings on the subject, as well as a large number of lavishly carved triumphal arches and victory columns.