ALL POLITIES ARE PRESSURE COOKERS. THEY DIFFER IN ALL SORTS OF ways – and many of the differences between them reflect the differences in the pressures they contain, in the way the ‘cooker’ has been designed or has found a durable shape, and in how they respond to the changing force and direction of the pressures. It is no longer fashionable to look with disdain at the special historical importance of such pressures within the American polity: we know all too well that comparable processes exist elsewhere. It remains true, however, that, within a changing context of society and culture, interest groups both public and private, are peculiarly alive and well within the American system.