Recurrent aphthous stomatitis (RAS)—otherwise known as canker sores, aphthous stomatitis, recurring oral aphthae, and recurrent aphthous ulceration—is a common cause of benign and noncontagious mouth ulcers, affecting about 20% of the general population. It is characterized by the appearance of an erythematous macule that develops into a painful, rounded or oval, ulcer covered with a yellow-gray fibrinous membrane with well-defined limits surrounded by an erythematous halo that can be scraped away. Three clinical subtypes of RAS have been established according to the magnitude, number, and duration of the outbreaks. The management of RAS should be based on identification and control of the possible predisposing factors, excluding possible underlying systemic causes. The use of a detailed clinical history is essentially coupled with complementary procedures such as laboratory tests, when needed. The lack of clarity regarding the etiology of aphthous ulcers has resulted in treatments that are mainly empiric, as there is no curative treatment available in most cases. This review examines the existing topical and systemic treatments for RAS and explores its etiology in depth.