The essay examines laughter from psychological, physiological, and social perspectives, beginning with the bodily mechanisms of smiling and laughing and their organic effects. It analyzes occasions and causes—tickling, nervous or reflex laughter, play, teasing, jokes and contests—and distinguishes varieties of the laughable, including novelty, bodily and moral deformity, breaches of order, small mishaps, indecency, pretence, ignorance, incongruity, and verbal wit. It evaluates competing philosophical theories of the ludicrous, surveys developmental and habitual aspects, notes benefits and excesses, and considers humour’s uses and value for individual feeling and social interaction.