Participating centers will include adult patients undergoing mechanical ventilation in the ICU during a 28-day period. Patients' data will be collected during the first 7 days in the ICU, or until ICU discharge. Follow up is until ICU discharge. The primary outcome includes two main ventilator settings, i.e., tidal volume and the level of positive end-expiratory pressure. Secondary endpoints are development of ARDS in patients without ARDS at the onset of mechanical ventilation, worsening of ARDS in patients with ARDS at the onset of mechanical ventilation, pulmonary infection, other pulmonary complications, need for tracheostomy, duration of ventilation, length of ICU stay and ICU mortality.