Amino acids are recognized as anabolic factors that induce protein gain by stimulating protein synthesis while inhib-iting proteolysis, and they are important substrates for the synthesis of various nitrogenous compounds. There is also increasing evidence that amino acids act as key regulators of metabolism through the control of major meta-bolic pathways in various tissues and organs. Elucidating the mechanisms involved in such regulation can provide a basis to optimize amino acid requirements and to control protein mass, body composition and meat quality while ensuring greater efficiency of production systems. However, with the aim of improving understanding of the re-sponse of chickens to nutrition, new approaches and technology (e.g. comparative physiology, genomics and model-ing) are also available to decipher mechanisms which could not be adequately analyzed a few years ago. This re-view presents the recent advances in this area generating original scientific knowledge and optimizing dietary amino acid provision (quantitative and qualitative) over time in relation to production targets. Emphasis is also placed on the limits of the information available for broiler chickens.