A cursory glance at a map, a university curriculum, or a government organization chart will confirm that man has a remarkable capacity for establishing arbitrary boundaries. Moreover, he has usually claimed a degree of sovereignty within those boundaries which he would energetically defend and, if possible, extend. We would continue to believe that we could reasonably afford our independent behavior except for the recent “discovery” that the human environment is not only a complex but also a finite system. Environmental problems, or, more particularly, the harmful effects of man's activities on his environment, challenge our exclusiveness and affect our existing territorial, disciplinary, and institutional boundaries simply because they transcend them. Of the many factors to be taken into account in dealing with environmental problems two have particular importance: the identification of the geographical level at which action can effectively be taken and the choice of the appropriate legal and institutional instruments to be employed.