BACKGROUND: Preterm birth is the leading cause of death in children younger than 5 years worldwide. Although preterm survival rates have increased in high-income countries, preterm newborns still die because of a lack of adequate newborn care in many low-income and middle-income countries. We estimated global, regional, and national rates of preterm birth in 2014, with trends over time for some selected countries. METHODS: We systematically searched for data on preterm birth for 194 WHO Member States from 1990 to 2014 in databases of national civil registration and vital statistics (CRVS). We also searched for population-representative surveys and research studies for countries with no or limited CRVS data. For 38 countries with high-quality data for preterm births in 2014, data are reported directly. For countries with at least three data points between 1990 and 2014, we used a linear mixed regression model to estimate preterm birth rates. We also calculated regional and global estimates of preterm birth for 2014. FINDINGS: We identified 1241 data points across 107 countries. The estimated global preterm birth rate for 2014 was 10.6% (uncertainty interval 9.0-12.0), equating to an estimated 14.84 million (12.65 million-16.73 million) live preterm births in 2014. 12. 0 million (81.1%) of these preterm births occurred in Asia and sub-Saharan Africa. Regional preterm birth rates for 2014 ranged from 13.4% (6.3-30.9) in North Africa to 8.7% (6.3-13.3) in Europe. India, China, Nigeria, Bangladesh, and Indonesia accounted for 57.9 million (41x4%) of 139.9 million livebirths and 6.6 million (44x6%) of preterm births globally in 2014. Of the 38 countries with high-quality data, preterm birth rates have increased since 2000 in 26 countries and decreased in 12 countries. Globally, we estimated that the preterm birth rate was 9x8% (8x3-10x9) in 2000, and 10x6% (9x0-12x0) in 2014. INTERPRETATION: Preterm birth remains a crucial issue in child mortality and improving quality of maternal and newborn care. To better understand the epidemiology of preterm birth, the quality and volume of data needs to be improved, including standardisation of definitions, measurement, and reporting. FUNDING: WHO and the March of Dimes.