Temporomandibular disorders (TMD) are one of the main sources of non-dental head and neck pain. Its pathology is not entirely understood and its etiology is complicated. Over time orthodontists have been more interested in relationship between occlusal variables orthodontic therapy & TMD and patient awareness and interest in oral health have expanded. Therefore the purpose of this book is to give a brief knowledge of the temporomandibular joint’s anatomy TMD and their complex etiology as well as their function in orthodontics.