In more than a dozen classified rulings, the nation's surveillance court has created a secret body of law giving the National Security Agency the power to amass vast collections of data on Americans. The rulings, some nearly 100 pages long, reveal that the court has taken on a much more expansive role by regularly assessing broad constitutional questions and establishing important judicial precedents, with almost no public scrutiny. The 11-member Foreign Intelligence Surveillance Court, known as the FISA court, was once mostly focused on approving case-by-case wiretapping orders. But since major changes in legislation and greater judicial oversight of intelligence operations were instituted six years ago, it has quietly become almost a parallel Supreme Court, serving as the ultimate arbiter on surveillance issues and delivering opinions that will most likely shape intelligence practices for years to come. In one of the court's most important decisions, the judges have expanded the use in terrorism cases of a legal principle known as the special needs" doctrine and carved out an exception to the Fourth Amendment's requirement of a warrant for searches and seizures. Unlike the Supreme Court, the FISA court hears from only one side in the case - the government - and its findings are almost never made public.