Micronutrients play a key role in many of the metabolic processes that promote survival from critical illness. For vitamins, these processes include oxidative phosphorylation, which is altered in the patient with systemic inflammation, and protection against mediators, in particular oxidants. Trace elements are essential for direct antioxidant activity as well as functioning as cofactors for a variety of antioxidant enzymes. Wound healing and immune function also depend on adequate levels of vitamins and trace elements (Table 6). Of extreme importance is the ease with which a deficiency state can develop in the critically ill because of decreased nutrient intakes and increased requirements. Daily intakes up to or exceeding many times the RDA usually are required. The enteral route is preferred, although, if not available, most of these agents can be given by the parenteral route. In that case, however, dose recommendations are less clear. Attention to micronutrients is paramount both in optimizing the nutritional management of the critically ill and in the overall management of these patients. It also is essential in promoting positive outcomes and decreasing complications.