Conscription is the compulsory enrollment of people to some sort of public service. While the service may be of any sort associated with the public, the term typically refers to enlistment in a country's military. Conscription dates back to antiquity and continues in some countries to the present day under various names. Used by the Royal Navy between 1664 and 1814, it was called impressment, or "the press". Most countries that maintain conscripts now refer to the practice as national service. In the United States, conscription ended in 1973 but remains alive in the national memory and is known colloquially as "the draft".

Conscription has historically focused on young men but the range of eligible ages may be expanded to meet national demand. In the United States, for instance, the Selective Service System drafted men for World War I initially in an age range from 21 to 30 but expanded its eligibility in 1918 to an age range of 18 to 45. In the case of a widespread mobilization of forces where service includes homefront defense, ages of conscripts may range much higher, with the oldest conscripts serving in roles requiring lesser mobility. Expanded-age conscription was common during the Second World War: in the United Kingdom, it was commonly known as "call-up" and extended to Age 55, while Nazi Germany termed it Volkssturm ("People's Storm") and included men as young as 16 and as old as 60. The term of service is often initially set but includes the prospect of indefinite extension based on national requirements.

Conscription can be controversial, because conscripts may have religious, political or moral reasons for refusing to serve. When governments decide to ignore these objections, protests have occurred and conscripts have evaded their enlistment by emigrating. Some selection systems accommodate these situations by providing forms of service outside of typical combat-operations roles or even outside of the military (e.g. Zivildienst in Germany, Austria and Switzerland).

As of the early twenty-first century, most nations[?] no longer conscript soldiers and sailors, relying instead upon professional militaries with volunteers enlisted to meet extraordinary demand for troops. The ability to rely on such an arrangement, however, presupposes some degree of predictability with regards to both warfighting requirements and the scope of hostilities. Many nations that have abolished conscription therefore still reserve the power to resume it during wartime or times of crisis.