Recurrent aphthous stomatitis (RAS; Aphthae; Canker sores), is a common oral mucosal disorder that presents as multiple, recurrent, small, round or ovoid ulcers with circumscribed margins and erythematous haloes on the oral mucosa. The triggering factors that cause precipitation of recurrent episodes in RAS patients seem to be as diverse and varied. This book includes an Introduction to the topic, Epidemiology, Pathophysiology & predisposing factors, Clinical features, Investigations, Management, and Summary. A Bibliography has also been included at the end.