In this thesis, I analyse the question of the responsibility of member states of international organisations for the violation of international obligations binding their organisation vis-it-vis non-member states either on the basis of general international or in an international agreement concluded by that organisation. For this purpose, I analyse, first of all, the relationship between international organisations and international law, and the conditions of their international responsibility in case of a violation these obligations. Then, I examine the current situation regarding international remedies, which can be invoked by third parties injured by such a violation. The analysis, in this regard, shows us the problems faced by third parties in this process. On the basis of the observations in the fonner chapters, the analysis then turns to the question of the possibility of holding member states of an international organisation responsible for the violation of international obligations by their organisation. In this respect, an examination of the relevant international treaties, international reports, case law and opinion of writers, show that it is generally accepted that states cannot absolve themselves from the consequences of a violation of an international obligation binding them toward non-member states by transferring certain competences to an organisation. Thus, they can be held internationally responsible if their organisation fails to fulfil these obligations in an appropriate manner. As far as the basis of this responsibility is concerned, I argue that the constituent treaty of an international organization is to be construed as a forum of member states, in which they express their intention to deal with certain common interest areas collectively. In other words, member states create common institutions and confer certain autonomy to them for dealing with the relevant areas of common interest, thus providing the organisation with competences in those areas. As a consequence, non-member states deal with member states in those areas via this institutional structure established by the constituent treaty. However, the constituent treaty remains as the basis of the relationship between member states and non-member states, despite the separate international personality of the organisation. Therefore, alth~ugh non-member states have the duty to respect the functioning of this treaty, they can In.voke th~ responsibility of member states secondarily if the organisation fails to fulfil ~ntematronal obligations, binding both the organisation and the member states, effectIvely and properly within the legal order established by the constituent treaty.