Foreign law, whether a subject of study in itself within the domain of comparative law, or invoked under a rule of conflict of laws to resolve a crossborder issue, is an essential library resource. In jurisdictions where foreign law must be pleaded and proved as a fact, it is up to the parties to demonstrate what that law is, in default of which the Anglo-American court will generally presume it to be the same as municipal law. In other, generally civil-law, jurisdictions it may be up the court to appoint an expert; foreign law may be treated either as law or as fact, depending upon the jurisdiction. Because family law, succession and donations are, in civil-law countries, largely ruled by personal law and because personal law may be determined by reference to facts of nationality, domicile, religion and ethnic identity, considerable academic sophistication is demanded of foreign and comparative law librarians. The escalating costs of legal materials and the difficulty of cataloguing and maintaining collections of rarely-used materials in hard languages pose additional obstacles. In the United States particularly, acquisition of foreign materials has perceptibly declined since the early 1980s. Only a handful of law libraries in the world possesses the financial, logistical, linguistic and technical wherewithal to aspire to collecting materials from all or most countries; for those, managing acquisition and selection is the main challenge. Collecting official gazettes, session laws and case reporters from many jurisdictions makes enormous demands upon space and record-keeping; microform collection is not in many cases an alternative. Where it is, it creates its own special demands.