Apnoea is defined as cessation of breathing with implicit pathophysiology. This review considers definitions of neonatal apnoea currently available and explores the evidence to support their use. For preterm and term infants, apnoea definitions appear arbitrary, are not supported by guidelines and vary from study to study. Although most alarms on infant breathing monitors are set to alert after a respiratory pause >20 s duration is detected, this time period is the equivalent of 17 missed breaths in a preterm infant. Apnoea is likely to be better defined by associated consequence than by pause duration alone in this age group; however, the degree of change in heart rate or oxygen saturation that defines a respiratory pause as pathological is yet to be defined. Further research is required to determine the characteristics that differentiate respiratory events of clinical consequence from normal respiratory variability in term and preterm infants.