Simplify, simplify! Henry David Thoreau. For writers of technical books, there can be no better piece of advice. Around the time of writing the first edition about a decade ago, there were very few monographs on this subject; today, there are possibly no less than 20. Based on critical inputs, this edition stands thoroughly revamped. New chapters on ventilator waveforms, airway humidification, and aerosol therapy in the ICU have been added. Novel software-based modes of ventilation are included. Ventilator-associated pneumonia has been separated into a new chapter. Many new diagrams and algorithms have been added. As in the previous edition, considerable energy has been spent presenting the material in a reader-friendly, conversational style. And as before, the book remains firmly rooted in physiology. My thanks are due to Madhu Reddy, Director of Universities Press.