The year 1925 was arguably the peak of literature’s centrality. There were more magazines, more journals, more reviews, more book news, and more book gossip than ever before or since. Literature’s rivals for cultural attention were on the rise—film was becoming a more significant part of people’s media diet, radio was just taking off, television technologies were advancing—but literature was still king. Even mediocre books got dozens of reviews, and the reviews were (most often) thoughtful and intellectually engaged. The belief that literary writing was an essential and consequential business was nearly universal. Modernist ferment continued to excite discussion while the pulp revolution in genre fiction—detective stories, science fiction, Westerns, romance—was booming. These popular books, even if sometimes condescended to, were also given thoughtful review attention. This encyclopedia was written as we approached the 100th anniversary of the annus mirabilis. In what follows, we can see the seeds of virtually every aspect of our cultural life, from art, literature, theater, and music to physics, philosophy, social science, and political discourse. The fear of environmental degradation, the corruption in our politics, the competing claims of utopianism and dystopia, the bitterly divided views on science, mass media, art, nature, justice, generations, community, freedom, sexuality, race, immigration—all can be seen in their budding or full-blown gore and glory in 1925. We have come far and not very far at all.