The work of breathing is undertaken by the respiratory muscles, the most important of which is the diaphragm. The diaphragm is prone to dysfunction in the newborn compared to older children and adults, due to inherent physiological, anatomical and histological characteristics. Prematurity is a risk factor for diaphragmatic dysfunction due to limited reserves, a smaller skeletal muscle mass and limited capacity to generate force and avoid fatigue. Respiratory muscle function in the newborn can be assessed with various methods including electromyography, maximal respiratory pressures, thoraco-abdominal asynchrony and bedside ultrasonography. Prolonged mechanical ventilation, hypercapnia and hypoxia, congenital anomalies and infection can negatively affect the respiratory muscles, while caffeine and synchronised modes of ventilation can have a positive effect on diaphragmatic function. Neurally adjusted ventilatory assist is a distinct ventilation mode, where the level of respiratory support is determined by the diaphragmatic electrical activity.