Diaries keep secrets, harboring our fantasies and fictional histories, sometimes taking the place of actual people. But in this age of social media, Sally Bayley points out, the role of the diary as a private confidante has been replaced by a culture of public self-disclosure. Tracing the evolution—and perhaps extinction—of the diary, Bayley examines the contributions of Samuel Pepys, Virginia Woolf, Henry David Thoreau, Sylvia Plath, and Anne Frank, while offering advice and encouragement to readers interested in beginning to write their own diaries.