Delivery before 37 weeks of gestation is a major worldwide public health concern, occurring in 10% of all births globally. This problem exists both in low-and middle-income countries (LMIC) and in high-income countries. In a 2012 report by WHO, March of Dimes, Save the Children, and The Partnership for Maternal, Newborn and Child Health-'Born Too Soon'-it was stated that in 2010, 15 million babies were born preterm, namely before 37 weeks of gestation. 1 Over 1 million of these preterm babies died. Surviving infants had an increased risk of learning disabilities, as well as visual and auditory problems. The magnitude of the problems is inversely related to gestational age at birth. For example, a linear decline in the need for special education can be shown for births from gestational week 24 to week 41. 2 At the time of the 'Born Too Soon' report, 1 only a few interventions were generally accepted: elimination of early elective deliveries; progesterone or progestational agents if a prior preterm birth had occurred; single embryo transfer in Assisted Reproductive Technologies (ART); cerclage for cervical insufficiency; cessation of smoking. If all of these guidelines were followed, however, the reduction in preterm birth was only a modest 9.6%-9.1%. 3As a result of these realities, the FIGO Working Group on Preterm Birth was initiated in 2014, a collaborative agreement between FIGO and the March of Dimes, both Non-State Actors (NSA) in official relations with WHO. Terms of reference included identification of risk factors, strategies to communicate clinical significance, and preparation of enduring educational material for use by member societies and for presentation at international FIGO meetings and elsewhere. These included FIGO World Congresses in Vancouver in 2015 and in Rio de Janeiro in 2018. Site-specific workshops and presentations were held elsewhere, in particular South America (Costa Rica, Uruguay). The success of these and other ventures have resulted in extension of the activities of Working Group. In 2016 the Working Group completed an exhaustive individual patient data meta-analysis encompassing 4.1 million births in California and four countries (Czech Republic, Sweden, New Zealand, Slovenia). 4 Of preterm birth pregnancies, 2/3 lacked a known biological basis. As result, attention expanded to elucidate the biological basis (etiology) of preterm birth. Enthusiasm for exploring the potential beneficial treatment with vaginal progesterone and 17-alpha OH progesterone caproate continued. Perturbations of the vaginal microbiome as a predisposing factor in preterm birth are perhaps one explanation for the markedly higher risk in African-Americans. Heritable factors have long been known to exist, and in 2017 a genomewide association study of 43 568 women discovered six genes of significance. 5 Work continues in other related fields-regulatory genes, glycobiology, maternal stress, sleep disturbance, and anatomic changes in the cervix and vagina. In this special section of IJGO, Preterm Birth Working Gro...