The ability of the cervix to function as a competent sphincter to retain the fetoplacental unit in utero until term is dependent on a complex set of biochemical, biophysical, and environmental events. The understanding of these interactions is limited at present and requires that cervical incompetence be a diagnosis of exclusion. Currently, differentiation of cervical incompetence from preterm labor is a major problem. Advances in ultrasonography, ambulatory uterine activity monitoring, cervical histomorphology, and biochemistry should improve the understanding of both normal and abnormal cervical and uterine function and may provide new techniques to distinguish between true cervical incompetence and preterm labor. Well-designed and strictly executed randomized clinical trials of cervical cerclage should answer the question of therapeutic efficacy for this popular technique when the diagnosis of cervical incompetence is made.