Seventy-three countries have some form of conscription or mandatory military service, including Austria, Israel, Mexico, Norway, Russia, and the United States. The rules vary greatly between countries.
Some countries do not practice active conscription but have a mandatory selective service system that certain age groups must register for so conscription can be implemented if necessary. Countries with a system like this include Bermuda and the United States.
Some countries have mandatory conscription for all men of a certain age but allow for more flexible terms of service if men volunteer instead. Men 18 years and older in Mexico are required to serve a year in the army if conscripted, and can only serve in the Air Force or Navy if they volunteer. Austria, Cyprus, Finland, Iran, and Switzerland all have mandatory military service but allow those conscripted to opt for a longer period of civilian or unarmed service instead.
Compulsory service is no more than one year in Austria, Bolivia, Brazil, Cape Verde, Colombia, Denmark, Estonia, Ecuador, Finland, Greece, Guatemala, Moldova, Mongolia, Norway, Paraguay, Russia, Taiwan, Tunisia, Turkey, Uzbekistan, and the United Arab Emirates. Service is no longer than 18 months in Algeria, Azerbaijan, Benin, Cambodia, Côte d'Ivoire, Egypt, Georgia, Kuwait, Laos and Turkmenistan.