This chapter aims to present a detailed discussion on the mechanism of childbirth. Labor during delivery is a normal physiological process that commences with uterine contractions of increasing frequency and regularity, duration and pain, which permit progressive effacement and dilatation of the cervix such that the fetus should be able to pass through the birth canal and be born. Uterine muscle, passage and passenger are three important factors for normal delivery, which are also discussed in this chapter. A detailed discussion on the cardinal movements of labor and pelvic phase of labor has been also provided in this chapter. Nine well-colored figures related to the mechanism of childbirth are presented in this chapter.