Santa Anna v. Frank was a United States Supreme Court case that dealt with the issue of whether a foreign government could be sued in a United States court. The case involved a dispute between the Mexican government, represented by General Antonio Lopez de Santa Anna, and a United States citizen, John Frank. Frank had been hired by the Mexican government to provide supplies and services during the Mexican-American War. After the war, Frank sued the Mexican government for payment of the services he had provided. The Supreme Court held that the Mexican government could not be sued in a United States court. The Court reasoned that the Mexican government was a foreign sovereign and, as such, was immune from suit in a United States court. The Court also noted that the United States had not entered into any treaty with Mexico that would allow for such a suit. The Court's decision in Santa Anna v. Frank established the principle of foreign sovereign immunity in the United States. This principle holds that foreign governments are immune from suit in United States courts unless the United States has entered into a treaty with the foreign government that allows for such suits. This principle has been applied in numerous cases since Santa Anna v. Frank and remains an important part of United States law.

Justice Field delivered the dissenting opinion in Santa Anna v. Frank, arguing that the majority had failed to consider an important precedent set by a previous Supreme Court case, The Santissima Trinidad. In this earlier decision, it was established that when a foreign government has been overthrown and replaced with another one, any debts or obligations of the former government are not binding on its successor unless they have been expressly assumed by it. Justice Field argued that since Mexico had never explicitly agreed to assume responsibility for Santa Anna's debt to Frank, there was no legal basis for requiring them to do so now. He concluded his dissent by noting that if such an obligation were imposed upon Mexico without their consent then "it would be difficult...to find any limit" as to what other countries could be held responsible for in similar circumstances.