For centuries, readers have inscribed books with handwritten marginal notes, or marginalia. These annotations can serve as ownership indicators, inscriptions, study notes, summaries, or they can facilitate what has been described as social reading in which two or more readers discuss the book’s contents in a margin-based conversation. Samuel Taylor Coleridge coined the term marginalia to encompass all such annotations, but the practice is as old as the printed book and even older: marginalia have been found in scrolls painstakingly copied down by medieval monks. Marginalia can serve as an aid to memory, a form of communication, a means of reflection, and a unique glimpse into the past. Attitudes towards the practice of annotating books range from the very negative to the very positive. Librarians tend to frown on the practice.