Establishing protective adaptive immunity during the perinatal period is critical for effective immune responses later in life. Preterm infants are susceptible to aberrant immune system maturation and inflammatory immune responses have been associated with the development of necrotizing enterocolitis (NEC) and bronchopulmonary dysplasia (BPD). Improving our understanding of how immune responses contribute to the pathogenesis of NEC and BPD may offer new opportunities for future treatment and prevention of these diseases.