It is, no doubt, a truism that in the relations of states treaties are matters of importance and frequent occurrence. The law of treaties, therefore, rightly occupies a central position in international law. Within this branch of the law, three large categories of rules may easily be distinguished relating, respectively, to the conclusion, to the interpretation, and to the termination of treaties. It is with some aspects of the first of these categories that the present study is exclusively concerned. In order that a treaty may be validly concluded on behalf of a state, two requirements are of fundamental importance: the first is that expressions of consent must have occurred; the second, that these expressions shall emanate from persons who are competent to give them. The original plan of the present study envisaged a full treatment of the rules of international law governing the two requirements referred to above. As the work proceeded, however, it became clear that no more than one of the topics could be treated within the framework of a thesis. Accordingly, the writer decided not to discuss the rules of international law relating to what constitutes an expression of consent to a treaty. The result of the writer's inquiry into the question whether, in cases of doubt, the signature of a treaty constitutes an irrevocable expression of consent, or ratification is required, is found in a published article, appended to the present study as Annex I. An inquiry into a cognate problem, namely, the need for unanimity in the revision of multilateral treaties, is also attached to this thesis as Annex II. Consequently, the present study is restricted to a systematic examination of those rules of international law which relate to the identification of those authorities in the state who are competent to express the final consent of the state to a treaty. The questions of the representation in contractual and treaty matters of subjects other than states, however, is not discussed. The present work deals with two distinct but interrelated problems. The first is that of the conditions under which the expressions of consent to a treaty of an authority or person are imputed to the state on whose behalf the authority or person purports to act. This is the question of identifying the competent treaty-making organ. The other problem is that of the conditions under which the expression of consent given to a treaty by an individual may be imputed to the treaty-making organ whose agent the individual purports to be. Both problems are of considerable difficulty. In the case of the second problem, the competence of agents, the difficulties are caused, chiefly, by the scant attention which the question has attracted. Material relevant to it has not been easily accessible, and the doctrinal discussion of the matter has hitherto been so limited that the present study may probably claim to be the first full treatment of the topic. By contrast, many of the difficulties relating to the problem of the competence of treaty-making organs, have been caused by the prolific treatment which it has been accorded at the hands of publicists. In order, therefore, to make some fresh contribution to this subject, the emphasis of this study has been placed on the investigation and discussion of the practice of states and the decisions of tribunals, both municipal and international. One consequence of this approach is to expose to criticism many of the views hitherto expressed on this subject; and it has, therefore, become necessary to attempt the formulation of a theory that is less contradicted by the practice of states than most existing theories seem to be. The study falls into three parts. Part I contains an examination of the problem of the competence of agents of treaty-making organs. Part II takes up the question of the competence of treaty-making organs generally. In Part III the same question is examined with special reference to states possessing constitutional regulations governing their treaty-making activities.