Repetitive, abnormal behaviour patterns are performed by tens, perhaps hundreds, of millions of animals worldwide: animals that live on farms and in laboratory animal facilities, stables, kennels, zoos, even in our homes. Our introductory chapter reviews the extent of research into this ‘stereotypic behaviour’ – traditionally defined as ‘repetitive, unvarying, with no obvious goal or function’ – since the book’s first edition was published in 1993. We illustrate the growing number of papers on captive animals, contrasting them with the