Naal Tsoos Saní, the “Old Paper” in the language of the Diné, is the Treaty of 1868 that ended the Navajo peoples’ forced relocation to the Bosque Redondo. Although it is the legal foundation of the modern Navajo Nation, its limits on traditional Diné sovereignty are still intensely debated. The 20-page document, recently displayed in the exhibit Nation to Nation: Treaties Between the United States and American Indian Nations at the Museum on the National Mall, is moving to the Navajo Nation Museum in Window Rock, Ariz., for the 150th anniversary of its signing.