Uterine contractions, decidual activation, and cervical competence comprise the fundamental components in contemporary models of the spontaneous preterm birth syndrome, but their relative importance and interactive pathways remain poorly defined. Moreover, the traditional concept that the cervix is either competent or incompetent has been challenged because cervical competence more likely functions along a biologic continuum. Cervical incompetence is a clinical diagnosis characterized by recurrent painless dilation and spontaneous midtrimester birth. Although the efficacy of cerclage for cervical incompetence has never been fully confirmed in randomized clinical trials, the role of cerclage has been expanded to include women with "risk factors" for spontaneous preterm birth or nonreassuring sonographic cervical findings in the mid trimester. Evidence from randomized trials suggests that cerclage has limited efficacy in women with risk factors for cervical incompetence. Results of both retrospective cohort series and randomized trials of cerclage in women with shortened cervical length are inconclusive. We believe that women with a prior early spontaneous preterm birth and shortened midtrimester cervical length represent an ideal population for the conduct of a randomized trial of cerclage, which is currently underway.