Early identification of Class II deep bite malocclusion is essential for a successful treatment outcome. Timely treatment with functional appliances is among the most effective treatment approaches available for the management of Class II malocclusion in growing subjects. The Medium Opening Activator belongs to a family of functional appliances known as activators. The aims of this article are to review the clinical management of the Medium Opening Activator and to describe a number of appliance modifications, including: (1) a method of stepwise advancement of the mandible using the same appliance; (2) modifications allowing transverse expansion of the maxillary posterior segments, and anterior movement of the maxillary labial segment in 1 appliance, negating the need for a prefunctional phase of treatment; and (3) placing mandibular fixed appliances early. A case report is described to demonstrate the benefits of the Medium Opening Activator. World J Orthodontics 2007;8:411.e1–9.