The author hopes that the present work may be of value to his colleagues in the legal profession who in one way or another are called upon to take part in the administration of international justice according to law. By a happy coincidence it was concluded on the tenth anniversary of the establishment of the Permanent Court of International Justice. The author is conscious of divers shortcomings. In particular he wishes that the survey of national law in Chapter II were more comprehensive and complete, and regrets that he was not per- mitted to examine the original documents in the case of Count- ess Szechenyi before the Czechoslovak-Hungarian Mixed Arbi- tral Tribunal. Investigation of the briefs and records of cases be- fore the United States Supreme Court might bring to light infor- mation not found in the reports. The author desires to thank his family and the authorities of Harvard University for enabling him to continue his legal studies until this book was written, and to thank for their stimulating suggestions the multitude of friends in many lands with whom he has had the benefit of valuable discussions in rem, not to speak of purely personal courtesies and indirect help. If there exists such a thing as international intellectual co-operation, this study may be regarded as one of its fruits.