Expansion of the maxillary arch to improve transverse inter-arch relationships during the primary or mixed dentition stage is considered early transverse treatment as part of a two-phase treatment protocol. Traditionally, early expansion has been used to correct posterior crossbite. More recently, it has been suggested that early transverse treatment may be beneficial, in the absence of posterior crossbite, to improve arch length deficiency, and to facilitate correction of skeletal class II malocclusions. In this article, the rationale for early transverse treatment in the presence and absence of posterior crossbite is reviewed.