ABSTRACT: Orthodontic treatment involving clear polyurethane aligners has started dominating the market. Although it has existed for almost two decades now, it is not indicated for all type of patients. Controversies exists in the aligners treatment indications. Some indicate that they should be used in orthodontic cases without skeletal disharmonies with mild crowding, whereas others have suggested that Invisalign may be suitable for even moderately complex orthodontic cases. In this review, a basic idea of the aligners and recent advances are discussed.