The respiration process involves two parts: the respiratory pump which ventilates the lung, and the lung which performs gas exchange. Respiratory failure appears when the respiratory system fails in the gas exchange functions or when the pump cannot ensure an adequate ventilation. The pump consists of the chest wall and the controllers of respiration, found in the central nervous system, which connect to the respiratory muscles through spinal cord and peripheral nerves. The diagnosis is based on arterial gas parameters (PaO2 less than 60 mmHg and/or PaCO2 higher than 45 mmHg). These values serve as a guidance, but the most important argument in clinical care is the clinical evaluation and the patient¿s history. Concerning the onset of the failure, it can be classified as acute, chronic or acute on chronic respiratory failure.The correct diagnosis and management of respiratory failure is an imminent need for the patient¿s life. By choosing the optimal treatment, oxygen delivery method and ventilation when needed you improve the survival and the quality of life of these patients.