External apical root resorption is an iatrogenic consequence of orthodontic treatment, although it may also occur in the absence of orthodontic treatment. Root resorption causes root shortening and breaks the integrity of teeth arch and this is very important for successful orthodontic treatment. Orthodontics is probably the only dental specialty that actually uses the inflammatory process as a means of solving functional and aesthetic problems. They should know the risk factors of root resorption and do everything to reduce the occurrence of root resorption. The aim of our review is to find, classify and estimate factors, that can initiate and induce root resorption during orthodontic treatment. The articles from 2002 to 2007 in English related to the topic were identified. Twenty four articles were selected for data collection. The severity and degree of root resorption associated with orthodontic treatment are multifactorial, involving host and environmental factors. The review shows that root resorption is significantly correlated with treatment duration, fixed appliance treatment, tooth structure, individual susceptibility, type of orthodontic tooth movement.