It is not in the least unusual, in newspaper accounts of a strike, riot, flood, or fire, to read that the governor has proclaimed martial law and summoned the militia to the threatened zone. However exaggerated such reports may be, they are evidence of a general belief that there exists some mysterious “martial law” which, when proclaimed, augments the powers of soldiers and paves the way for heroic measures. Nor are these notions wholly fanciful. For such a proclamation may indeed be followed by an extraordinary régime in which the military authority will issue regulations for the conduct of the civil population, troops may be called upon to take life, and perhaps the individuals accused of fomenting trouble will be held without authority of a court, or in some cases may even be tried by a military tribunal. Quite likely these severe measures will receive the approval of public opinion. Yet it is surprising that a people ordinarily rather legalistic should have evinced so little disposition to inquire what rules of law, if any, govern the exercise of these military powers. To answering that unasked query the present study is addressed.