The need for uniformity and harmony in international trade can be expected to lead to growth of international transactions subject to the CISG, UNIDROIT Principles, and PECL. In a summary fashion as to the relationship between the three instruments, to some extent it can be described briefly that they enable themselves to supplement each other and fit well with each other as part of the multi-layered approach that is becoming dominant, rather than compete or claim to displace the other harmonizing projects. In so far as the three instruments seem to have their own raison d''être they not only do not compete with each other but may actually fulfil very important functions side by side. Particularly, so as to preclude an easy resort to the domestic law indicated by the conflict of law rule of the forum, the two sets of Principles serve a gap-filling role for the interpretation of CISG contracts; they endorse and promote many of the principles outlined in the CISG. Although, in this instance, the articles are not drafted in an identical or substantially similar manner, it is nonetheless possible to identify some supports and the two Principles can be used to: (1) interpret the CISG; (2) answer unresolved questions that fall within the scope of the CISG; or (3) resolve issues that are not addressed in the CISG.
　
　Finally, one must become aware of the existence and basic content of different concepts contained in these instruments, because they will be shaping the rules for contractual dealings in the future. Particularly, one must be on the lookout for superficial harmony which merely mutes a deeper discord and for verbal conflict which hides a fundamental identity of aim. In both cases the key lies in the conceptual presuppositions of each system or family of systems. The deeper discord escapes notice because the same formula means different things according to the frame-work in which it is read; the fundamental agreement on the end to be achieved is not seen because the conceptual routes which lead that to end are different.
　　　　
　
　1.3 MAJOR SOURCES OF INFORMATION
　
　In view of their close relationship, these instruments merit a comparative study in order to understand their similarities and differences, at least with respect to certain matters. In so doing, every conscientious author would refer to an extensive amount of sources of information available for the three instruments. In this contribution, I carry on my analysis depending mostly on the followings which bear the greatest significance: as for the CISG, it is above all the Secretariat Commentary on the 1978 Draft of the CISG (hereinafter "Secretariat Commentary"). To the extent it is relevant to the Official Text, the Secretariat Commentary is perhaps the most authoritative source one can cite. It is the closest counterpart to an Official Commentary on the CISG.
　
　Indeed, the drafting history of the Convention is a legitimate and valuable aid in the interpretation of the Convention''s provisions. The CISG has a rich and detailed legislative history. The challenge is not paucity of material, but an overabundance of travaux préparatoires spread over thousands of pages of un-indexed volumes, located in sources we are not used to accessing, with frames of reference (article numbers) that generally differ from those of the CISG.
　　　　 The most recent and, generally, the most important segment of the legislative history of the CISG is contained in the Official Records of the Conference (Vienna, 10 March - 11 April 1980
　　　　 ; hereinafter "O.R."), which is very useful as a guide to the rationale behind many of the Articles.
　
　As for the UNIDROIT Principles, unlike the CISG to whose text there is no official commentary, each article of the Principles is accompanied by the Official Commentary. The Official Commentary consists of comments and, where appropriate, factual illustrations intended to explain the reasons for the black letter rule and the different ways in which it may operate in practice. The comments are an integral part of the UNIDROIT Principles, all the more so as sometimes they not only explain but to a certain extent even supplement the black letter rule.28 Like the commentary to the UNIDROIT Principles, the Commentary to the PECL contains comments and, where appropriate, factual illustrations helping explain the text. In addition, the Notes contained in the Commentary to the PECL identify civil law and common law antecedents and related domestic provisions.

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