The maxillary quad-helix appliance is a commonly used approach for treatment of maxillary arch constriction and/or posterior crossbite. Concern over excessive force generation during rapid maxillary expansion led to its development and use in growing children. The purpose of this article is to present the clinical application and therapeutic considerations regarding use of the quad-helix appliance in the slow maxillary expansion of mixed dentition cases. Considerable evidence is presented supporting such early expansion and factors for case selection are identified when considering this a treatment option.