Nutritional support is an integral part of the treatment of the critically ill patient. Enteral feeding is viewed as the first line of feeding of the intensive care unit (ICU) patient and has many benefits in maintaining the functionality of the intestine. When we consider the nutritional support of the ICU patient, we first define the calorie-protein target, and then then determine the route of feeding, timing for starting the feeding, and the most appropriate formula. Usually enteral feeding is started in the early stages of ICU hospitalization, after 24-48 h, in order to maintain the gut barrier functionality and support the immune system response. The patient population in the ICU is very heterogenic and the appropriate formula should be chosen with care. A right formula could positively affect clinical outcomes. Many available formulas, including formulas enriched with specific pharmaconutrients such as arginine, glutamine, fish oil, and antioxidants have proven to be beneficial. In this chapter, we will discuss the known properties and the different approaches of various formulas according to clinical conditions and will also estimate the possible complications of enteral feeding.