Two questions are basic to military justice: who can be brought to trial in a military court, and for what? Courts-martial are exceptional courts; their jurisdiction over individuals is limited because it has always been understood that military justice has as its purpose the maintenance of order and discipline within the armed forces. ‘Who is subject to trial by court-martial?’ shows that this general rule has been tested time and time again. Some countries employ courts-martial or other military tribunals to prosecute civilians with no connection whatever to the military and others have “tail jurisdiction” over people after they leave military service. Cases for and against when military justice should be used are also presented.