Abstract: Liberalism is a term employed in a dizzying variety of ways in political thought and social science. This essay challenges how the liberal tradition is typically understood. I start by delineating different types of response—prescriptive, comprehensive, explanatory—that are frequently conflated in answering the question “what is liberalism?” I then discuss assorted methodological strategies employed in the existing literature: after rejecting “stipulative” and “canonical” approaches, I outline a contextualist alternative. Liberalism, on this (comprehensive) account, is best characterised as the sum of the arguments that have been classified as liberal, and recognised as such by other self-proclaimed liberals, over time and space. In the remainder of the article, I present an historical analysis of shifts in the meaning of liberalism in Anglo-American political thought between 1850 and 1950, focusing in particular on how Locke came to be characterised as a liberal. I argue that the scope of the liberal traditionexpanded during the middle decades of the twentieth century, such that it came to be seen by many as the constitutive ideology of the West. This capacious (and deeply confusing) understanding of liberalism was a product of the ideological wars fought against “totalitarianism” and assorted developments in the social sciences. Today we both inherit and inhabit it.