This book is both a work of intellectual history and a contribution to legal philosophy. It represents a serious and philosophically sophisticated guide to modern American legal theory, demonstrating that legal positivism has been a misunderstood and underappreciated perspective through most of twentieth-century American legal thought. The broad scope of this book ensures that it will be read by philosophers of law, historians of law, historians of American intellectual life, and those in political science concerned with public law and administration.