General means of international law interpretation are codified by the Vienna Convention on the Law of Treaties since 1969. Particular provisions are to be found in articles 31 and 32 of the Convention. It stems form these particular provisions of the Vienna Convention, that other than main means of interpretation should be used only after all main interpretative means fail. It does not mean that various documents serving as evidence of preparatory works for so called historical interpretation or bunch of interpretative principles or presumptions can be considered as totally meaningless. Present article does not deal with main interpretative provisions anchored in article 31 of the Vienna Convention on the Law of Treaties; attention is paid to the interpretation in international law generally, then, in a limited way, to the historical interpretation, and to some interpretative principles and presumptions in the WTO law, namely to the principle of effective interpretation and to the doctrine of legitimate expectations. Article tries to analyse some aspects of international law interpretation within the WTO system. It also attempts to prove that WTO law forms and integral part of the international law in general, irrespective of its relatively autonomous development. Not only WTO law forms a part of general international law as such, it is considered nowadays even to be one of the leading elements in its further development through the newly established dispute settlement mechanism. It is quite obvious that WTO Panels and appellate Body are one of the most frequently used adjudicatory bodies in international law. It is quite clear then, that their decisions can have strong impact on the development of the international law as such. Not only they have proved in their decision making, that WTO law does not form a system separate from the general international law. Appellate Body decisions serve as model for decision making in other areas of international law. It was then quite natural to demonstrate the use of some interpretative means on WTO decision making.