Tail biting is both a costly and welfare-reducing problems for grower/finisher pigs. This paper is a recent comprehensive review of papers on this topic. It covers the stages in the development of tail biting, how it can be assessed, and how it leads to associated problems of infection, disease, weight loss and death. Three theories are presented on its development: a learned behaviour; a normal behaviour that becomes excessive; and, a redirected behaviour (eg. exploration that becomes directed to the tail). Risk factors associated with the pigs themselves include: genetics, gender, age and weight, and health status. External risk factors include: rearing environment, rooting materials, indoor climate, outdoor climate, stocking density and herd size, floor type, feeding system, and food. Various treatments and preventative measures are discussed. Tail biting results in a reduction in the welfare of the bitten pig, but probably also indicates poor welfare in the biting pig as well.