Introduction Preterm birth is a significant public health and obstetric problem. While accounting for only 6–10% of all births, preterm delivery is responsible for 70–85% of neonatal morbidity and mortality. Approximately three fourths of these preterm births occur secondary to preterm labor or preterm rupture of membranes. Despite the advances in neonatal care and technology, these statistics have not changed dramatically over the last several decades. Obstetricians have approached this issue from preventative and therapeutic standpoints. Preventative measures and methods of identifying women at increased risk for preterm labor have met with limited success. These methods include risk scoring indices, home uterine activity monitoring, ultrasound evaluation of cervical length, serial digital cervical examinations, fetal fibronectin, and salivary estriol testing to name a few. Pharmacologic therapies have been used with the goal of decreasing the morbidity and mortality of prematurity by manipulating the process of parturit ion. This article will focus on the pharmacologic inhibition of labor with an initial overview of the contemporary understanding and approach to preterm labor, goals and criteria for labor inhibition, overview of the mechanisms of parturition and myometrial contractility, followed by a systematic and evidence-based approach to currently used tocolytic agents including betaadrenergic receptor agonists, magnesium sulfate, prostaglandin inhibitors, calcium channel blockers, oxytocin antagonists, and nitric oxide donors.