Malnutrition is a common problem in critically ill patients, which is associated with an increase in ICU and hospital mortality. Previous studies have found an prevalence of malnutrition in hospitalized patients of 40-50%, with associated weight loss of approximately 5 kilograms during hospital admission. This reflects unrecognized nutritional problems from the caring physician point of view. Critically ill patients experience an increased basal metabolic rate due to severe stress which can lead to malnourishment and malnutrition in some stages of hospitalization. Therefore, adequate nutritional supplement is one of the important modalities in critical care to improve the intensive care outcome. Caring physicians need to know about the processes of nutritional assessment, daily energy requirements and monitoring processes of nutritional support. This review article presents an overview of nutritional support in the critically ill patient, including nutritional assessment, estimation of daily energy requirements, route of nutritional support and nutritional status monitoring.