The energy requirements for maintenance and production of poultry species are defined as nitrogen-corrected apparent metabolizable energy, with data based on research conducted primarily with cereals and soybean meals. At the present time, the number of raw materials, most of them with a high fiber content, has increased, a trend that is not expected to change in the near future. Consequently, the role of the different components of ingredients and diets, namely proteins, lipids, and carbohydrates, as supplier of effective energy for maintenance and productivity of the birds, needs further evaluation. In addition, factors such as dietary fiber content, and the physicochemical characteristics, feed form, and particle size of the diets affect the feed intake and the development of the gastrointestinal tract of the birds, and thus, the growth and profile of the existing microbiota. In practice, all these effects are confounded and therefore, new research is needed to better understand and evaluate their effects on chicken health and productivity.