The number of transfers of critically ill patients within and between hospitals has been continuously increasing throughout the entire evolution of intensive care medicine. Even the transport of patients between two departments in one hospital can be hazardous. Arguably, the highest risk is that of ensuring a patent airway and adequate ventilation. This chapter discusses the process of transferring ventilated patients, and examines portable ventilators in some detail. The standard of patient monitoring during the transfer is essentially the same as that prior to transfer, although in some cases it may actually require increasing the monitoring. In essence, transport ventilators can be divided into two basic groups. The first group is pneumatically driven ventilators that require high-pressure oxygen to drive the ventilator. The second group of ventilators generates tidal volume with electrically powered internal compressors. The chapter also presents a discussion on difficult transfer and transport scenarios.