Recurrent aphthous stomatitis is the most common oral mucosal ulcer disease. It causes severe pain and occurs repeatedly, causing discomfort in daily routine activities. The description of etiology is varied and none of the explanations given so far are satisfactory. Clinically this condition presents itself in three forms: major, minor and herpetiform ulcers. Causes for the ulcers could be related to host and / or environment. Host factors include genetic, nutritional deficiency, immune dysregulation and stress which can again be multifactorial. Environmental factors include trauma (both physical and chemical) and infections. There are several clinical syndromes which are associated with RAS like Behcet__ampersandsignrsquo;s syndrome. There are several causes acting together in initiating formation of ulcer unlike a single etiological factor as was thought previously. This means combination of host and environmental factors are essential not only for triggering the ulcer but also for an increase in size. The severity of etiological factors to which an individual is exposed would decide the type of ulcer. Identification of the trigger for a particular individual seems to be important in management of the disease. Hence understanding etiopathogenesis for recurrent aphthous stomatitis would be helpful in formulation of individualized treatment modalities. This review is intended to understand the cause and pathogenesis of recurrent aphthous stomatitis.