A much-needed defense of liberalism--what it is, why it is under threat, and why we need it more than ever--from one of our most important political thinkers today. More than at any time since World War II, liberalism is under pressure, even siege. On the right, some have given up on liberalism. They hold it responsible for the collapse of the family and traditional values, rampant criminality, disrespect for authority, and widespread immorality. On the left, some are turning their backs on liberalism. They think that it lacks the resources to handle the problems posed by entrenched inequalities, racism, sexism, corporate power, and environmental degradation. But those opposed to liberalism do not depict it accurately; they offer a caricature, and they neglect its history. In On Liberalism, former advisor to Presidents Obama and Biden and New York Times-bestselling author Cass Sunstein offers a timely and clear understanding of liberalism--of its core commitments, of its breadth, of its internal debates, of its evolving character, of its promise--and why we need it more than ever. He also shows how and why liberalism has been, and should be, appealing to both the left and the right. The book begins with a manifesto on behalf of liberalism, and then goes on to explore the central idea of "experiments of living," to which a liberal constitutional order gives pride of place. From there, it discusses John Stuart Mill and Friedrich Hayek, defining liberal thinkers; the rule of law as liberals understand it; freedom of speech (including the place of lies and falsehoods within that freedom); free markets, economic liberty, and regulation; Franklin Delano Roosevelt's Second Bill of Rights, with its social and economic guarantees; and finally, the concept of opportunity. Never more urgently needed, On Liberalism moves the conversation well beyond the reductive and inflammatory political sound bites of our moment and advances a compelling argument on behalf of liberalism as the foundation of freedom and self-government.