Conscription, also known as the draft in American English, is the practice in which the compulsory enlistment in a national service, mainly a military service, is enforced by law. Conscription dates back to antiquity and it continues in some countries to the present day under various names. The modern system of near-universal national conscription for young men dates to the French Revolution in the 1790s, where it became the basis of a very large and powerful military. Most European nations later copied the system in peacetime, so that men at a certain age would serve 1 to 8 years on active duty and then transfer to the reserve force.

Conscription is controversial for a range of reasons, including conscientious objection to military engagements on religious or philosophical grounds; political objection, for example to service for a disliked government or unpopular war; sexism, in that historically only men have been subject to the draft; and ideological objection, for example, to a perceived violation of individual rights. Those conscripted may evade service, sometimes by leaving the country, and seeking asylum in another country. Some selection systems accommodate these attitudes by providing alternative service outside combat-operations roles or even outside the military, such as siviilipalvelus (alternative civil service) in Finland and Zivildienst (compulsory community service) in Austria and Switzerland. Several countries conscript male soldiers not only for armed forces, but also for paramilitary agencies, which are dedicated to police-like domestic-only service like internal troops, border guards or non-combat rescue duties like civil defence.

As of 2025, many states no longer conscript their citizens, relying instead upon professional militaries with volunteers. The ability to rely on such an arrangement, however, presupposes some degree of predictability with regard to both war-fighting requirements and the scope of hostilities. Many states that have abolished conscription still, therefore, reserve the power to resume conscription during wartime or times of crisis. States involved in wars or interstate rivalries are most likely to implement conscription, and democracies are less likely than autocracies to implement conscription. With a few exceptions, such as Singapore and Egypt, former British colonies are less likely to have conscription, as they are influenced by British anti-conscription norms that can be traced back to the English Civil War; the United Kingdom abolished conscription in 1960. Conscription in the United States has not been enforced since 1973. Conscription was ended in most European countries, with the system still being in force in Scandinavian countries, Finland, Switzerland, Austria, Greece, Cyprus, Turkey and several countries of the former Eastern Bloc.

Around the reign of Hammurabi (1791–1750 BC), the Babylonian Empire used a system of conscription called Ilkum. Under that system those eligible were required to serve in the royal army in time of war. During times of peace they were instead required to provide labour for other activities of the state. In return for this service, people subject to it gained the right to hold land. It is possible that this right was not to hold land per se but specific land supplied by the state.

Various forms of avoiding military service are recorded. While it was outlawed by the Code of Hammurabi, the hiring of substitutes appears to have been practiced both before and after the creation of the code. Later records show that Ilkum commitments could become regularly traded. In other places, people simply left their towns to avoid their Ilkum service. Another option was to sell Ilkum lands and the commitments along with them. With the exception of a few exempted classes, this was forbidden by the Code of Hammurabi.

See Early Roman army.

Under the feudal laws on the European continent, landowners in the medieval period enforced a system whereby all peasants, freemen commoners and noblemen aged 15 to 60 living in the countryside or in urban centers, were summoned for military duty when required by either the king or the local lord, bringing along the weapons and armor according to their wealth. These levies fought as footmen, sergeants, and men at arms under local superiors appointed by the king or the local lord such as the arrière-ban in France. Arrière-ban denoted a general levy, where all able-bodied males age 15 to 60 living in the Kingdom of France were summoned to go to war by the King (or the constable and the marshals). Men were summoned by the bailiff (or the sénéchal in the south). Bailiffs were military and political administrators installed by the King to steward and govern a specific area of a province following the king's commands and orders. The men summoned in this way were then summoned by the lieutenant who was the King's representative and military governor over an entire province comprising many bailiwicks, seneschalties and castellanies. All men from the richest noble to the poorest commoner were summoned under the arrière-ban and they were supposed to present themselves to the King or his officials.

In medieval Scandinavia the leiðangr (Old Norse), leidang (Norwegian), leding, (Danish), ledung (Swedish), lichting (Dutch), expeditio (Latin) or sometimes leþing (Old English), was a levy of free farmers conscripted into coastal fleets for seasonal excursions and in defence of the realm.