The multidisciplinary care of a critically ill patient is a real challenge. In addition to the haemodynamic and respiratory instability, the metabolic balance is seriously altered in such a patient. The catabolism and a simultaneous compromised nutritional intake induce a proteino-energy deficit with negative consequences. The assessment of caloric needs for the critically ill patient is still a matter of debate. The lack of, as well as the excess, of energy supply is associated with a worse patient’s outcome, emphasizing the importance of determining the appropriate energy target as soon as possible. Indirect calorimetry is considered as the gold standard in clinical practice. The energy needs may be otherwise estimated by predictive equations, adjusted with corrective factors, but these are often inaccurate. Experts recommend simple formulae based on the patient’s actual body weight. Once the energy target is determined, the appropriate nutritional delivery route must be chosen. Enteral nutrition is considered to be the first choice in case of a functional digestive tract. However, the enteral route is often associated with a cumulative deficit of energy intake, which may worsen the malnutrition of the critically ill patient and increase the incidence of secondary complications (mortality, morbidity, duration of mechanical ventilation, and length of hospital stay). Supplemental parenteral nutrition is one of the alternatives proposed to prevent this energy deficit. Raising awareness of health care teams on the potentially serious consequences of malnutrition and their adherence to nutritional protocols is an integral part of the process of quality of care.