Humidity in the form of molecular water vapor is an essential requirement for intubated patients, and can be beneficial to nonintubated patients receiving CPAP or oxygen therapy. There are many different types of humidification devices but they generally consist of a humidity generator (or water reservoir) and humidity delivery system (or breathing circuit). Humidifiers that generate aerosols may provide adequate humidity, but they also provide a transport mechanism for contaminants and may deliver excess water to the airways. An ideal system generates the required amount of humidity, in the form of water vapor, at the correct temperature, and transports it to the patient without the loss of either heat or moisture. The most effective way to achieve this is to use a large heated water surface for the generator, and heating elements within the delivery system to prevent condensation. This system can be configured to provide optimal humidity for both intubated and nonintubated patients from the neonatal to the adult intensive care unit. Heated humidifiers have no contraindications and can be used on any patient requiring ventilatory assistance or supplemental oxygen.