CHIEF JUSTICE ROBERTS, with whom JUSTICE KENNEDY joins, dissenting. 

The Court begins by deciding a different case, “initiallytreat[ing] the document before us as if it were an ordinary contract between private parties.” Ante, at 6. The “document before us,” of course, is nothing of the sort. It is instead a treaty between two sovereign nations: the UnitedKingdom and Argentina. No investor is a party to the agreement. Having elided this rather important fact formuch of its analysis, the majority finally “relax[es] [its]ordinary contract assumption and ask[s] whether the factthat the document before us is a treaty makes a criticaldifference to [its] analysis.” Ante, at 10. It should come as no surprise that, after starting down the wrong road, themajority ends up at the wrong place.

I would start with the document that is before us and take it on its own terms. That document is a bilateral investment treaty between the United Kingdom and Argentina, in which Argentina agreed to take steps to encourage U. K. investors to invest within its borders (and the United Kingdom agreed to do the same with respect toArgentine investors). Agreement for the Promotion and Protection of Investments, Dec. 11, 1990, 1765 U. N. T. S. 33 (Treaty). The Treaty does indeed contain a completed agreement for arbitration—between the signatory countries. Art. 9. The Treaty also includes, in Article 8, certain provisions for resolving any disputes that might arise between a signatory country and an investor, who is not aparty to the agreement.