“Shines a floodlight on a topic that has been cloaked in obscurity . . . a landmark work in both intellectual history and political theory” (The Wall Street Journal). Philosophical esotericism—the practice of communicating one’s unorthodox thoughts “between the lines”—was a common practice until the end of the eighteenth century. Despite its long and well-documented history, however, esotericism is often dismissed today as a rare occurrence. But by ignoring esotericism, we risk cutting ourselves off from a full understanding of Western philosophical thought. Walking readers through both an ancient (Plato) and a modern (Machiavelli) esoteric work, Arthur M. Melzer explains what esotericism is—and is not. It relies not on secret codes, but simply on a more intensive use of familiar rhetorical techniques like metaphor, irony, and insinuation. Melzer explores the various motives that led thinkers in different times and places to engage in this strange practice, while also exploring the motives that lead more recent thinkers not only to dislike and avoid this practice but to deny its very existence. In the book’s final section, “A Beginner’s Guide to Esoteric Reading,” Melzer turns to how we might once again cultivate the long-forgotten art of reading esoteric works. The first comprehensive, book-length study of the history and theoretical basis of philosophical esotericism, Philosophy Between the Lines is “a treasure-house of insight and learning. It is that rare thing: an eye-opening book . . . By making the world before Enlightenment appear as strange as it truly was, [Melzer] makes our world stranger than we think it is” (George Kateb, Professor of Politics, Emeritus, at Princeton University). “Brilliant, pellucid, and meticulously researched.” —City Journal