Mechanical ventilation is a common form of support in the modern day intensive care unit (ICU). In order for the clinician better to understand and apply mechanical ventilation, it is important that they understand the physiological principles of ventilation. This review describes these basic concepts; parameters of mechanical ventilation, high frequency ventilation and non-invasive ventilation. An overview of ventilatory strategies for four common diseases seen in paediatric and neonatal ICUs will be discussed.