“A diary is not only a text: it is a behaviour, a way of life, of which the text is a by-product", says the French theorist Philipe Lejeune. From ancient Babylon to journalling today, politicians' jottings and the notes made by eighteenth century writers like Mary Hamilton and Fanny Burney. Matthew Sweet discusses diaries with curator Irving Finkel, literary historian Sophie Coulombeau, political commentator Michael Crick and writer Oliver Burkeman, whose latest book is Meditation For Mortals, plus the philosopher Maximillian De Gaynesford.