"Federal courts are frequently called upon to evaluate foreign law in a variety of contexts--from routine breach of contract and tort claims to complex cases implicating the judicial branch's role in international affairs. In Animal Science Products, Inc. v. Hebei Welcome Pharmaceutical Co. Ltd., the Supreme Court announced the standard of deference for U.S. federal courts to apply when considering a foreign government's interpretation of its own law. Prior to the Court's ruling, federal courts took a range of approaches on the degree of deference given to a foreign government's official explanation of its domestic law. Some courts viewed a foreign nation's interpretation as effectively binding (at least as long as it was reasonable), but others were willing to deviate from the nation's position if it was inconsistent with prior statements or not supported by affidavits and expert testimony. In Animal Science Products, Inc., the Supreme Court unanimously held that federal courts must give 'respectful consideration' to a foreign government's interpretation, but they are not 'bound to defer' to that position."
CRS Legal Sidebar, LSB10166
Federation of American Scientists: http://www.fas.org/sgp/crs/index.html