Preterm birth is a leading cause of peripheral morbidity and mortality. The national rate of prematurity approaches 11%. In spite of widespread tocolytic use, the preterm birth rate has actually increased over the past 30 years in the United States. Preterm birth appears to have a multifactorial etiology. Leading theories include infectious, inflammatory or ischemic insult to the uteroplacental barrier, activation of the fetal hypothalamic-pituitary pathway, decreased cervical competence, and pathologic uterine distention. Multiple biochemical and biophysical markers have been studied for their potential to correctly identify women at risk of preterm delivery. Of these, fetal fibronectin and endovaginal ultrasound examination of the cervix have proven effective in predicting which symptomatic women are actually at low risk of preterm birth. Salivary estriol is being studied as a marker for preterm labor and delivery and it too will likely be found to be a reliable risk identifier in a high risk population. However, home uterine activity monitoring has not been shown to decrease the frequency of preterm birth or its neonatal complications.