Conscription is in place for nine of Europe's Nato states: Denmark, Estonia, Finland, Greece, Latvia, Lithuania, Norway, Sweden and Turkey.
In Turkey, which has the second largest military in the security alliance after the US, men between the ages of 20 and 41 are obliged to do military service for between six and 12 months.
By comparison, Norway conscripts both men and women, generally for 12 months.
Croatia plans to reintroduce conscription next year - it will become mandatory for men aged 19 to 29 to undergo two months of basic military training.
Other Nato members do not conscript but have professional militaries.
The UK, which rivals France or Germany in conventional military strength (and is the only Nato state in Europe along with France to have nuclear weapons), relies on a professional army.
It is unique among Nato members for recruiting minors - 16-year-olds may join with parental consent.
Albania, Czechia, Hungary, Italy, Luxembourg, Montenegro, North Macedonia, Portugal, Slovakia, Slovenia and Spain also have professional militaries.
Iceland has no regular military forces, though its Coast Guard performs some defence tasks.