The 1980 United Nations Convention on Contracts for the International Sale of Goods (CISG or Vienna Convention), conceived for worldwide acceptance, sets forth a uniform set of rules aimed at regulating some of the issues that, in an international sales contract, are likely to arise between the parties to such international transaction. The extent to which the substantive solutions that the Vienna Convention provides with the aim of filling in gaps within international sales contracts, are to achieve the standing of a predictable, global, and uniform legal background for these contracts, is the question to be treated in this paper from the analysis of the treatment that the said Convention dispenses to international trade usages as a part of the legal regime of an international sale transaction to which the CISG technically applies and the practical consequences deriving from that treatment. The study proceeds first with some considerations as to the notion of "transnational law" in order to see how the Vienna Convention and international trade usages fit together within the same notion. Second, the thesis presents the main features of international sales of goods followed by a narrative of their regulation by international conventions.