The United States recognizes the Vienna Convention as a codification of customary international law. The United States Department of State considers the Vienna Convention "in dealing with day-to-day treaty problems" and recognizes the Vienna Convention as in large part "the authoritative guide to current treaty law and practice." Frankowska, supra, at 298 (quoting Assistant Legal Advisor for Treaty Affairs at the Department of State and Secretary of State Roger's Report to the President, Oct. 18, 1971, 65 Dep't St. Bull. 684, 685 (1971)). In addition, the Department of State has stated that where it has not recognized the Vienna Convention as codifying customary international law, it has adopted it as customary law going forward. See id. at 300.

    United States courts have also cited the Vienna Convention as an authoritative codification of customary international law. See Sale v. Haitian Centers Council, Inc., 509 U.S. 155, 191, 113 S.Ct. 2549, 125 L.Ed.2d 128 (1993) (Blackmun, J., dissenting) (citing Article 31.1); Weinberger v. Rossi, 456 U.S. 25, 29 n. 5, 102 S.Ct. 1510, 71 L.Ed.2d 715 (1982) (citing Article 2(1)(a)); Aquamar, S.A. v. Del Monte Fresh Produce N.A., Inc., 179 F.3d 1279, 1296 n. 40 (11th Cir.1999) ("Although the United States is not a party to the Vienna Convention, it regards the substantive provisions of the Vienna Convention as codifying the international law of treaties.") (quoting Kreimerman v. Casa Veerkamp S.A. de C.V., 22 F.3d 634, 638 n. 9 (5th Cir.1994)); Tseng v. El Al Israel Airlines, Ltd., 122 F.3d 99, 104-05 (2d Cir.1997) (citing Articles 31 and 32), rev'd on other grounds, 525 U.S. 155, 119 S.Ct. 662, 142 L.Ed.2d 576 (1999); Haitian Ctrs. Council, Inc. v. McNary, 969 F.2d 1350, 1361-62 (2d Cir.1992) ("[P]rinciples of treaty construction are themselves codified, in Article 31 of the Vienna Convention.... We have previously applied the Vienna Convention in interpreting treaties, Day v.Trans World Airlines, Inc., 528 F.2d 31, 36 (2d Cir.1975) (Warsaw Convention), ... as has the United States Department of State."), rev'd on other grounds sub nom., Sale v. Haitian Ctrs., 509 U.S. 155, 113 S.Ct. 2549, 125 L.Ed.2d 128 (1993). In addition, the Restatement relies on the Vienna Convention as a codification of the customary international law of treaties, see Restatement Introduction ("[C]odification of branches of international law by international bodies ... have provided authoritative text as a source for restatement of some topics. This is the case, for example, with respect to the international law of treaties, largely codified in the Vienna Convention on the Law of Treaties."), and confirms that "[t]he international law restated here ... represents ... the rules that an impartial tribunal would apply if charged with deciding a controversy in accordance with international law," id.

We therefore treat the Vienna Convention as an authoritative guide to the customary international law of treaties.