Bedside ultrasonography can be very useful in the evaluation and management of mechanically ventilated patients. In intensive care units the role of ultrasound is not limited to diagnosis but can be used as a guide for management of mechanical ventilation from early stages to weaning. To obtain a comprehensive functional evaluation of critical care patients during mechanical ventilation, chest ultrasonography should include the examinations of the lungs, heart, and diaphragm. Lung ultrasound is an emerging and increasingly used imaging tool to investigate both in a semiquantitative and quantitative way lung aeration during mechanical ventilation, thus helping physicians to determine the best ventilator settings to reexpand collapsed lung regions, avoiding pulmonary stress and strain. Echocardiography is important to assess right and left ventricular function, to guide ventilation strategies such as low-plateau pressures, best positive end-expiratory pressure, pronation, and permissive hypoxia and hypercapnia. Monitoring the effects of mechanical ventilation on cardiac-lung interaction may prompt lung-heart protective ventilation strategy to avoid right ventricular failure, which is correlated with worse outcomes. Moreover, during weaning from mechanical ventilation chest ultrasound may give much information to the clinician, because weaning failure is due to cardiac reasons in a number of patients. Early echocardiography assessment and monitoring of weaning may lead to therapeutic interventions to improve left ventricular diastolic function and choose the best timing. Furthermore, ultrasound evaluation of diaphragm excursion and contractility may predict weaning failure.