Of the modern political labels that emerged and spread in the early-nineteenth-century “Age of Revolutions,” none is more difficult to pin down than “liberal.” Conservatism, socialism, and nationalism all take manifold forms, but liberalism is the most protean of all. Liberals have been royalists and republicans, anti-clericals and Catholics, individualists and communitarians, opponents and supporters of government action in society and the economy. There have been liberal advocates of universal suffrage and of restricted voting rights, liberal defenders of capitalism and liberal critics of it, liberal imperialists and liberal foes of empire. Do the terms liberal and liberalism point to one thing or many? Is there a solid core to being liberal that gives substance to all its variations, or does it owe its diffusion to some fickle fluidity that allows it to take on the shapes people and circumstances impose on it? These questions point to yet another, especially critical for historians: Just who should count as a liberal? Self-declared anti-liberals have sought to tar each other with the label, while some among those who claim it for themselves contest the right of others to bear it.