Humour is a funny thing - everyone knows it but no-one knows what it is. This book addresses the question `What is humour?' by first untangling the definitions of humour, amusement and funniness before then providing a new theory of humour which draws upon recent research in philosophy, psychology, linguistics and neuroscience. The theory is built up without assuming any prior knowledge and illustrated through humorous examples in a way that is both educational and entertaining for anyone curious to know what makes things funny. This makes the book an accessible illumination on joking matters from dinner tables to online platforms to comedy clubs.