This paper, part of the "Born Too Soon" supplement, reviews the global epidemiology of preterm birth and its burden, emphasizing the need for improved data systems to track trends and program effectiveness. Preterm birth, defined as births before 37 weeks of gestation, affects 11.1% of all live births globally, with rates increasing in most countries. Direct complications account for one million deaths annually, and preterm birth is a risk factor in over 50% of neonatal deaths. Long-term complications are common, with severity increasing with decreasing gestational age and quality of care. Economic costs are significant, including immediate neonatal intensive care and long-term health needs. Preterm birth is a syndrome with various causes, including spontaneous and provider-initiated births. Consistent recording of all pregnancy outcomes and standard definitions are crucial for understanding and monitoring trends. Context-specific solutions are needed to prevent preterm birth and reduce rates worldwide. Strengthened data systems are essential to track trends and program effectiveness, coupled with improved antenatal, obstetric, and newborn care to increase survival and reduce disability among preterm infants.This paper, part of the "Born Too Soon" supplement, reviews the global epidemiology of preterm birth and its burden, emphasizing the need for improved data systems to track trends and program effectiveness. Preterm birth, defined as births before 37 weeks of gestation, affects 11.1% of all live births globally, with rates increasing in most countries. Direct complications account for one million deaths annually, and preterm birth is a risk factor in over 50% of neonatal deaths. Long-term complications are common, with severity increasing with decreasing gestational age and quality of care. Economic costs are significant, including immediate neonatal intensive care and long-term health needs. Preterm birth is a syndrome with various causes, including spontaneous and provider-initiated births. Consistent recording of all pregnancy outcomes and standard definitions are crucial for understanding and monitoring trends. Context-specific solutions are needed to prevent preterm birth and reduce rates worldwide. Strengthened data systems are essential to track trends and program effectiveness, coupled with improved antenatal, obstetric, and newborn care to increase survival and reduce disability among preterm infants.