Deciding whether a contract of sale is an international transaction or not and according to which criteria is an inescapable task, not only for private international law(PIL) but also for the instruments aiming to create uniform substantive contract law. The paper reviews the different solutions from the 1930s to the development of the last decades, from the first drafts of the International Institute for the Unification of Private Law ('UNIDROIT') on international sales to the Draft Common European Sales Law. Of course, the Vienna Sales Convention ('CISG'), as a successful international instrument,is also given special emphasis in this comparative and historical analysis. Althoughduring the past century of unification, the definition of international character becameclearer and simpler, much however depends on how broadly or narrowly legislators wishto define the scope of the uniform substantive law to facilitate the acceptance andratification of an international convention. A further specific question is whether uni-form law should apply to all international sales (universal application) or only to international transactions linked to Contracting States. The paper also analyses the different positions on this issue