An introduction to annotation as a genre—a synthesis of reading, thinking, writing, and communication—and its significance in scholarship and everyday life. Annotation—the addition of a note to a text—is an everyday and social activity that provides information, shares commentary, sparks conversation, expresses power, and aids learning. It helps mediate the relationship between reading and writing. This volume in the MIT Press Essential Knowledge series offers an introduction to annotation and its literary, scholarly, civic, and everyday significance across historical and contemporary contexts. It approaches annotation as a genre—a synthesis of reading, thinking, writing, and communication—and offers examples of annotation that range from medieval rubrication and early book culture to data labeling and online reviews. After introducing such ideas as paratext, multimodality, and intertextuality, the authors discuss the affordances and types of annotation in a variety of contexts. Annotation that provides information, for example, can be a time stamp on a text message or a footnote to a text; annotation that shares commentary can be praise (or the opposite) on Rate My Professors or the texts in the Hebrew Talmud; and annotation that aids learning can be added by experts for students or by students for their peers. Far from being an arcane practice of scholars, annotation allows readers to respond to their texts, interact with various forms of media, and make meaning with and from this everyday activity.