Oxygen is the most commonly used therapy in neonatal nurseries as an integral part of respiratory support. The goal of oxygen therapy is to achieve adequate delivery of oxygen to the tissue without creating oxygen toxicity. Oxygen must have been given to newborn preterm babies more than any other medicinal product in the past 60 years. Despite this, we still know very little about how much oxygen these babies actually need, or how much oxygen is safe to give, especially in the first few weeks of life. Recent observational studies have raised concerns that giving oxygen to target the saturation at "physiological" levels in newborn preterm babies may do more harm than good, but to date, clinicians have not been able to resolve the uncertainties surrounding optimum oxygen therapy.