Functional jaw orthopedics derives its active force form the muscles of mastication. All orthodontists are compulsive mycologists. Myology is both interesting and captivating. All the essential motor functions of the body require healthy and able musculature. This chapter starts by discussing the basic types and classification of muscles, histology, physiology of muscle contraction and moves on to the development of muscles and with special emphasis on craniofacial muscles. The culmination of the chapter is the role of various aspects of muscle like thickness, function like bite force, etc. on research.