The causes of bark stripping and browsing by squirrels, rabbits, hares, voles and edible dormice in forests and woodlands are reviewed. Population density and tree characteristics are the most significant causes of damage, but habitat characteristics, particularly where they contribute to higher densities, are also important. There are still aspects of some forms of damage which are not well understood. Agonistic behaviour is thought to be as or more important than feeding in contributing to grey squirrel damage, but the difficulties of making observations in the wild have made it impossible to verify the role of behaviour. Improvements in understanding of all forms of damage could come from more investigations on tree quality (including the role of phenols, terpenes and other nutritional components) and the relationships between habitat variables and damage. Methods of predicting the risk of damage are discussed.