Prior restraints have historically been perhaps the least tolerated infringements on free speech in Anglo-American law. In its most common form, a prior restraint is a judicial order preventing the media from publishing material already in its hands. In the 18th century, Sir William Blackstone stated the legal aversion to prior restraints in its classic formulation: "The liberty of the press is indeed essential to the nature of a free state; but this consists in laying no previous restraints upon publications, and not in freedom from censure for criminal matter when published."1 Prior restraints were regarded as pernicious because they stopped speech from ever being heard. A scheme of subsequent punishment might discourage potential speakers, but prior restraints allowed ideas to be silenced before they even saw the light of day. As Chief Justice Burger put it: "If it can be said that a threat of criminal or civil sanctions after publication 'chills' speech, prior restraint 'freezes' it at least for the time."2