Preterm birth is increasingly recognised as a determinant of chronic respiratory disease across the life course. In this Series on prematurity-associated lung disease (PLD), we introduce the concept of PLD as a unifying framework for the diverse pulmonary consequences of preterm birth. Historically, most attention has focused on extremely preterm infants (<28 weeks of gestation) who develop bronchopulmonary dysplasia (BPD), yet not all infants with BPD have long-term morbidity. Conversely, those born very (28-31 weeks), moderate (32-33 weeks), or late (34-36 weeks) preterm also have increased risk for developing lung disease. Multiple factors beyond BPD-including gestational age and intrauterine growth restriction-contribute to PLD development. Recently described PLD phenotypes include prematurity-associated obstructive lung disease, prematurity-associated preserved ratio impaired spirometry, and prematurity-associated dysanapsis. Each phenotype reflects distinct early-life exposures and mechanisms, with differing implications for prognosis. Defining these phenotypes provides a foundation for personalised monitoring and targeted therapeutic strategies.