The editors of this Review have had the felicitous idea to mark its 50th anniversary with a special issue devoted to the time factor in international law, with one contribution devoted to the apparently declining importance of travaux préparatoires in the interpretation of treaties. Under Article 32 of the Vienna Convention on the Law of Treaties, the preparatory works of a treaty are only to be consulted in a limited number of circumstances, and then only as supplementary means of interpretation: when application of the general rule (combining a textual approach with an interpretation in light of the treaty's object and purpose) does not lead to satisfactory results. Under Article 31, paragraph 2, of the Vienna Convention, travaux préparatoires do not even qualify as part of a treaty's context; clearly, the Vienna Convention envisages but a very limited role for a treaty's preparatory works. Yet, most international lawyers will almost automatically include a discussion of preparatory works in legal argument, and will consider it vital to do so: an argument without paying due regard to a treaty's drafting history is an incomplete argument. It is this ambivalence which I hope to explore.