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14 “assisted by an interpreter [they] employed.” Jones v. Meehan, 175 U. S. 1, 11 (1899).

Put together, these insights have long influenced the interpretation of Indian treaties. “The language used in treaties with the Indians should never be construed to their prejudice.” Worcester v. Georgia, 6 Pet. 515, 582 (1832) (McLean, J., concurring). Rather, when a treaty’s words “are susceptible of a more extended meaning than their plain import,” we must assign them that meaning. Ibid. Our duty, this Court has repeatedly explained, lies in interpreting Indian treaties “in a spirit which generously recognizes the full obligation of this [N]ation.” Tulee v. Washington, 315 U. S. 681, 684–685 (1942); see also United States v. Winans, 198 U. S. 371, 380–381 (1905); Choctaw Nation v. United States, 119 U. S. 1, 27–28 (1886). We sometimes call this interpretive maxim—really just a special application of ordinary contract-interpretation principles—the Indian canon. See F. Cohen, Handbook of Federal Indian Law §2.02, p. 119 (N. Newton ed. 2005); R. Collins, Never Construed to Their Prejudice: In Honor of David Getches, 84 U. Colo. L. Rev. 1, 6–7 (2013).

With time, too, these interpretive insights have yielded some more concrete rules. First, courts must “give effect to the terms” of treaties as “the Indians themselves would have understood them.” Minnesota v. Mille Lacs Band of Chippewa Indians, 526 U. S. 172, 196 (1999); see also Tulee, 315 U. S., at 684. Second, to gain a complete view of the Tribes’ understanding, courts may (and often must) “look beyond the written words to the larger context that frames the Treaty.” Mille Lacs Band, 526 U. S., at 196. That includes taking stock of “the history of the treaty, the negotiations, and the practical construction adopted by the parties.” Choctaw Nation v. United States, 318 U. S. 423, 432 (1943). Third, courts must assume into those treaties a duty of “good faith” on the part of the United States to “protec[t]” the Tribes and their ways of life. See Washington