Despite the publication of a number of studies over recent years looking at energy delivery and outcomes in the critically ill population we remain uncertain how best to determine optimal calorie delivery for our patients. The concept that energy delivery should match energy consumption is plausible and intellectually attractive bu Broadly speaking clinicians can be divided into 3 categories according to their approach on energy delivery to the critically ill. Some believe that optimal clinical outcomes are achieved by closely approximating energy consumption i.e. providing full calorie requirement, usually around 2000kcal/d for the standard sized adult. This position is supported by a number of observational studies, however, patients usually only receive about 60% of what they are prescribed. Some believe that attempting to provide full feeding exposes the patient to the risk of overfeeding and that ‘permissive’ underfeeding is safe and better tolerated in critically ill patients where gastrointestinal function is frequently deranged. Interestingly, recent data suggest that the patient group potentially most at risk of overfeeding are those who are malnourished at presentation. Finally, some believe that the amount of energy delivered during ICU stay has little impact on recovery. Only when the ICU stay becomes unusually prolonged may the amount of energy delivered become important. There is evidence to suggest that some nutrition should be given enterally from early in the ICU stay to provide gastrointestinal mucosal protection and improve subsequent gut function. In recent years there have been several randomised controlled trials addressing energy delivery but they have unfortunately given conflicting results. Furthermore, these studies have had a number of limitations including: being underpowered to show an effect on survival; open to bias because of being open-labelled; most have not delivered full energy requirements so the effect of this on outcomes remains uncertain. It is hoped that many of these issues will be addressed in the currently recruiting TARGET trial which will be completed next year.t, while energy delivery can be measured with indirect calorimetry, this is not a technique that lends itself to routine clinical care. Accurate measurement or calculation of day to day energy expenditure is not currently routinely possible. Delivery of nutrition is an important supportive activity in the ICU. Patients generally receive less than prescribed nutritional needs and there is no robust evidence as yet to suggest that this is deleterious to outcomes.