With every other major nation converted to the metric system or committed to conversion, eventually the United States will also adopt this system as the predominant common language of measurement. Developing trends in international trade indicate such a course, and a growing majority of U. S. businessmen and educators favors conversion to the metric system. The key decisions now facing the United States pertain to planning and timing. The changeover, most people agree, should be carefully coordinated and could take place over a transition period of ten years, more or less, under reasonable guidelines designed to encourage maximum voluntary participation by all sectors. If the changeover to predominant metric usage is guided by a “Rule of Reason,” the costs and difficulties of conversion can be minimized. Immediate steps should be taken to stress the teaching of the metric system in our schools and to promote a more vigorous and influential role by American industry in the setting of international engineering standards.