The place of the critical care unit activation, within a field hospital, deployed to disaster area is challenged. Criteria used in the decision-making of activation are facility capabilities, combined with the event characteristics itself. The development of current concepts of critical care has allowed the survival of patients with advanced illness and injury. Since this discipline involves maximal lifesaving interventions, it was kept out of the scope of most field hospitals deployments among the world. Providing critical care is challenged by lack of medical information, and by the fact that a field ICU team, based on the reserve forces is gathered from few different acting ICUs of regular hospitals. Bridging those gaps is mandatory for a proper operation of a field ICU. As for the medical team, the nursing team is generally based on the reserve forces. It is gathered from various civilian and military facilities, with different daily practices and routines. Unifying those in the short time available, until full operation of the field ICU, can be an obstacle. Imaging modalities, laboratory services, documentation, and equipment issues are to be considered when planning for the field ICU activation. All those, including complex ethical difficulties to be solve, in spite of language and cultural barriers, are discussed in this chapter.