The incidence of head and neck cancer is increasing rapidly. It is fast becoming a global health priority with an incidence of about 780,000 new cases per year. The treatment of oral cancer is primarily aimed at maximizing survival and loco-regional control while trying to preserve normal oral function and quality of life. A symptom related to oral cancer, which previously has not been paid much attention to, is trismus. 'Trismus' indicates a muscular dysfunction or tonic contraction of the muscles of mastication which could result from various factors, leading to difficulty in mouth opening. In oral cancer, this can have a profound effect on the patient's quality of life thereby reducing the effects of rehabilitation and overall well-being. This book evaluates trismus, a significant consequence of oral malignancies or its surgical and radiotherapy treatment, or both, to facilitate its early diagnosis and help in timely intervention and planning of preventive strategies.