Class II malocclusion is one of the most common problems around the globe affecting around one-third of the patients who come for orthodontic  treatment .Twin block appliance from its inception and evolution itself has been widely accepted as a more competent Class II corrector compared to earlier bulky monoblock appliances. Functional appliances can be used successfully in growing patients with certain skeletal Class II patients. Twin block appliance is very effective in a growing patient. The successful use of this appliance in the treatment of skeletal Class II malocclusion is based upon factors such as; age of patient, compliance of the patient and other case selection criteria. This appliance is very successful in a patient with a retrognathic mandible and well aligned arches with a positive VTO. This efficiently enables the mandibular forward positioning and improves the profile. This case report is of a 14-year-old adolescent female patient having a Class II skeletal pattern and a recessive mandibular jaw who was treated  with a fixed Twin block appliance. The profile changes and treatment results were demonstrated. In permanent dentition, twin block appliance produces a similar effect as in mixed dentition phase. With proper case selection and good patient cooperation, we can obtain a significant result with William Clark’s twin block appliance.