Few episodes in recent history have aroused as much controversy as the United Nations military operations in the Congo. This controversy has no simple, straight-forward, and uniform explanation. Part of the explanation is to be found in the successes and failure of the operation itself; part in its labyrinthine international ramifications. But the most important explanation lies in its significance as a precedent. The ability of the Organization to take "e;collective measures"e; to maintain law and order within the territory of a Member State, albeit as a means of preserving international peace, was demonstrated, challenged and criticized. So much has been reported of the details and so varied has been the commentary that only the most intrepid spirit would venture something more with which to detain interested parties. The present study does not pretend to uncover new data so as to complete or correct the his- torical record; it attempts, rather, to reflect on what has already been brought out and, against that background of factual knowledge, to indi- cate and examine the legal problems involved. In so doing, it has been necessary to be ruthless in deciding what are central issues and in re- jecting what is often interesting but probably peripheral.