The main components of total energy expenditure are energy expenditure for maintenance or basal metabolic rate, the thermic effect of food or diet-induced energy expenditure (DEE), and the energy cost of physical activity or activity-induced energy expenditure (AEE). This chapter describes methods to measure energy expenditure, determinants of energy expenditure and the application of energy expenditure measurements for the evaluation of intake methods. The methods section includes techniques, methods to measure separate components of daily energy expenditure, and measuring substrate utilisation. The determinants section describes the subject characteristics involved, such as body composition, age and gender, and behavioural aspects including food intake and physical activity. Evaluation of intake methods is based on principles of energy requirement and techniques to assess energy homeostasis. In the adult population, the prevalence of overweight has increased and at the same time reported energy intake and %energy from fat have decreased.