Trismus or lockjaw also referred to as a restricted mouth opening. It is a common problem in patients with head and neck cancer undergoing radiotherapy. These Patients with trismus often experience difficulties in performing activities of daily living, such as eating, drinking and laughing. In India, mouth cancer is on the rise. The first-line treatment for Head, neck, and face cancer patients is radiotherapy, chemotherapy and surgical excisions. But no treatment comes without any complication. All these established treatments affect temporomandibular joint structure including muscles and ligaments. As per our knowledge literature is lacking about the exact prevalence of trismus in HNF cancer patients in a rural part of India. Hence this book was written on research that was aimed at finding out the prevalence of trismus in HNF cancer patients undergoing radiotherapy at the tertiary care hospital. If the prevalence is found physiotherapy intervention can be planned for treatment for trismus. Many pieces of evidence are available for role of exercises in the treatment of cases with trismus.