This study of the President’s use of emergency powers grew out of research and discussions in Washington, D. C., and at Harvard, the University of California, and other institutions. In one sense, it is a sequel to Dr. Cotter’s study of emergency powers in Great Britain, prepared under Harvard’s Sheldon Travelling Fellowship during the academic year 1951-52. In preparing a political science course at the University of California’s Riverside campus, one of the most significant gaps in available sources and treatises about the Presidency concerned the vast range of power, generally called emergency powers, available to the Chief Executive should he choose to follow the prescription used by many predecessors, notably F.D.R. Both authors have, of course, profited from the monumental work of Professor Edward S. Corwin, whose classic study, _The President: Office and Powers_ remains the outstanding work in the field. Professor Robert S. Rankin’s study, _When the Civil Law Fails_, contained valuable historical data of particular importance. Both authors have also had the inestimable privilege and opportunity of studying under Professor Charles Fairman, now at Harvard Law School. Professor Fairman’s study, _The Law of Martial Rule_, was very helpful in providing the historical setting for government under military control. The authors were fortunate in having read Professor Fairman’s paper delivered at the National War College, “A Post-Atomic Attack Situation,” wherein it is clearly brought forth that a complete plan and pattern for dealing with a nuclear attack must be worked out that does envisage the restoration of civil government to the nation as quickly as circumstances permit, should the cold war ever turn into an all-out nuclear holocaust. While the original work on the manuscript was completed before either of the authors came to Washington, both have benefitted from the experience of working in the Pentagon, the Commission on Civil Rights, the Republican National Committee and the U. S. Senate. One is apt to view the executive branch of government from a slightly different perspective, once having been associated with “the Hill.” And, while the Congress may feel powerless to act against a determined Chief Executive, the power of the purse still provides the most effective of all the “checks and balances” in our national government, except in time of war. The Fund for the Republic provided the authors with a grant-in-aid in 1955 to begin work on the book, although the Fund had no contact or association with the authors during the preparation of the manuscript. Parts of some chapters have previously appeared as article in the _Western Political Quarterly_ and _The Journal of Politics_, and the authors wish to acknowledge their appreciation at being able to reproduce all or parts of these articles.