It is during labor that the most dramatic changes to the cervix are apparent, yet the cervix begins its process of adapting early on in pregnancy. From an anatomic perspective, the gravid cervix is changed little in the beginning of pregnancy. It is strikingly less muscular than the rest of the uterus and its connective tissue is comprised essentially of collagen fibers and a matrix rich in proteoglycans. Cervical maturation begins imperceptibly during pregnancy but does not become noticeable until shortly before labor. These changes result from biochemical modifications of the cervical constituents with dissolving of collagen fibers and changes in the respective levels of different proteoglycans. The regulation of this maturation is still poorly understood; steroid hormones, prostaglandins, and collagenases have all been implicated. The effacement and dilatation of the cervix occur with labor. Effacement corresponds with thinning and opening of the internal os and dilatation corresponds with opening of the external os. These phenomena are passive, resulting from physical pressure from fetal engagement under the effects of uterine contractions. Our material understanding of cervical maturation and dilatation are still insufficient, for although we are better and better able to guide the induction and course of labor, it still is impossible for us to arrest premature cervical maturation in the setting of a threatened abortion or premature delivery.