Mechanical ventilation has been shown to cause ventilation-induced lung injury by at least two mechanisms. First, using a low lung volume allows the repeated opening and closing of small airways and alveoli. This is associated with high shear forces on the lung interstitium and alveolar surfactant depletion, both of which result in ventilation-induced lung injury. To reduce this low-volume injury, the use of positive end-expiratory pressure (PEEP) is advocated, though the ideal amount of PEEP continues to be the topic of intense study. Second, the use of too much PEEP and/or the use of supraphysiologic tidal volumes have been shown to cause ventilation-induced lung injury by overdistention of alveoli. Historically, alveolar overdistention has been a concern when plateau pressure (Pplat) is >30 cm H₂O. Although much attention is often given to high peak airway pressure, it is Pplat that reflects alveolar pressure, value most associated with ventilation-induced lung injury. Two approaches to limiting alveolar overdistention are (a) to reduce tidal volume until plateau pressure ≤30 cm H₂O during assist volume control (AC) ventilation or (b) to limit inspiratory airway pressure to ≤30 cm H₂O during pressure-regulated volume control (PRVC) ventilation. The astute clinician will be able to understand (a) the differences between AC and PRVC ventilation modes, (b) that alveolar pressures ≤30cm H₂O might not be uniformly safe, and (c) the appropriate strategy that limits both low volume and overdistention lung injury.