The book begins with the design and construction of Alberto Manguel's own library at his house in western France -- a process that raises puzzling questions about his past and his reading habits, as well as broader ones about the nature of categories, catalogues, architecture and identity. Exploring these themes with a deliberately unsystematic brilliance, Manguel takes us to the great Library at Alexandria, and Michelangelo's Laurentian Library in Florence; we sit with Jorge Luis Borges in his office at the National Library in Argentina, travel with donkeys carrying books into the Colombian hinterland, and discover the Fihrist, a chaotic and delightful bibliographic record of medieval Arab knowledge. There seem to be no limits to Manguel's learning, or his ability to illuminate his investigations with magical, telling details from the past. Thematically organized and beautifully illustrated, this book considers libraries as treasure troves and architectural spaces; it looks on them as autobiographies of their owners and as statements of national identity. It examines small personal libraries and libraries that started as philanthropic ventures, and analyzes the unending promise -- and defects -- of virtual ones. It compares different methods of categorization (and what they imply) and libraries that have built up by chance as opposed to by conscious direction. Although it is encyclopedic (and discusses encyclopedias assembled by Diderot and fifteenth-century Chinese scholars alike) and full of concrete historical analysis (including a brief investigation of the prejudices underlying the Dewey Decimal System) this book is animated throughout by a gentle, even playful sensibility: it is governed by the browser's logic of association and pleasure, rather than the rigid lines of scholarly theory. After all, everything in a library is connected: "As the librarians of Alexandria perhaps discovered, any single literary moment necessarily implies all others." In part this is because this is about the library at night, not during the day: this book takes in what happens after the lights go out, when the world is sleeping, when books become the rightful owners of the library and the reader is the interloper. Then all daytime order is upended: one book calls to another across the shelves, and new alliances are created across time and space. And so, as well as the best design for a reading room and the makeup of Robinson Crusoe's library, this book dwells on more "nocturnal" subjects: fictional libraries like those carried by Count Dracula and Frankenstein's monster; shadow libraries of lost and censored books; imaginary libraries of books not yet written.