attributes make regional lung function monitoring particularly useful whenever there is a need to improve oxygenation or CO2 elimination and when therapy changes are intended to achieve a more homogenous gas distribution in mechanically ventilated patients. EIT lung imaging can resolve the changes in the regional distribution of lung volumes between e.g. dependent and non-dependent lung regions as ventilator parameters are changed. Thus, EIT measurements may be used to guide specific ventilator settings to maintain lung protective ventilation for each patient. Besides the applicability of EIT in the ICU, first studies with spontaneously breathing patients reveal further promising applications. The high temporal resolution of EIT allows regional assessment of common dynamic parameters used in pulmonary function testing (e.g. forced expiratory volume in 1 second). Additionally, specially developed image fusion methods overlaying functional EIT-data with morphological patient data (e.g. CT or MRI images) may be used to get a comprehensive insight into the pathophysiology of the lungs, which might be useful for patients with obstructive lung diseases (e.g. COPD, CF). After many years of lung EIT research with provisional EIT equipment or series models manufactured in very small numbers, two commercial systems for lung EIT have recently entered the medical technology market: Dräger's PulmoVista® 500 and Swisstom AG's Swisstom BB2. Both models are currently being installed in intensive care units and are already used as aides in decision-making processes related to the treatment of patients with acute respiratory distress syndrome (ARDS). The increasing availability of commercial EIT systems in ICUs will show whether the promising body of evidence obtained from animal models will apply to humans as well (EIT-guided lung recruitment, selection of optimum PEEP levels, pneumothorax detection, prevention of ventilator associated lung injury (VALI), etc.). This would be highly desirable, given that recent studies suggest that 15% of mechanically ventilated patients in the ICU will develop acute lung injury (ALI) with attendant progressive lung collapse and which is associated with a reportedly high mortality of 39%. Just recently, the first prospective animal trial on EIT-guided mechanical ventilation and outcome could demonstrate significant benefits in regard to respiratory mechanics, gas exchange, and histological signs of ventilator-associated lung injury. In addition to visual information (e.g. regional distribution of tidal volume), EIT measurements provide raw data sets that can be used to calculate other helpful information (e.g. changes of intrathoracal gas volume during critical illness) – however, such parameters still require careful evaluation