Yznaga del Valle v. Harrison et al. was a United States Supreme Court case that dealt with the issue of whether a foreign judgment could be enforced in the United States. The case involved a dispute between Yznaga del Valle, a Mexican citizen, and Harrison et al., a group of American citizens. Yznaga del Valle had obtained a judgment against Harrison et al. in a Mexican court, and sought to enforce the judgment in the United States. The Supreme Court held that the Mexican judgment could not be enforced in the United States. The Court reasoned that the Mexican court did not have jurisdiction over the American citizens, and thus the judgment was not valid in the United States. The Court also noted that the Mexican court did not have the authority to enforce its judgment in the United States, and thus the judgment could not be enforced in the United States. The Court's decision in Yznaga del Valle v. Harrison et al. established that foreign judgments cannot be enforced in the United States unless the foreign court had jurisdiction over the parties and the authority to enforce its judgment in the United States. This decision has been cited in numerous subsequent cases, and remains an important precedent in the area of foreign judgments.

In Yznaga del Valle v. Harrison et al., the Supreme Court was tasked with determining whether a Mexican land grant, made by Mexico prior to its cession of Texas to the United States in 1848, could be enforced against subsequent purchasers from the United States government. The majority opinion held that it could not because such grants were extinguished upon annexation and therefore did not pass title to any property within Texas. Justice Field dissented on this point, arguing that under international law treaties are binding contracts between nations and should be respected even after one nation has been annexed by another. He argued that since Mexico had granted these lands before they were annexed into the US, those rights should still remain valid for their original owners or their heirs despite having passed through several hands over time. As such he concluded that Yznaga's claim should have been upheld as valid and enforceable against all subsequent purchasers of her land grant from the US government