<p>Global interest has emerged for the implementation of reduced-protein diets for meat chickens. The necessity of their development stems from environmental impacts and health and welfare concerns surrounding current meat-chicken production. Reduced crude-protein diets are possible with the increasing affordability of supplemental crystalline amino acids. Supplementing broiler feed with methionine, lysine and threonine is common practice in industry and has enabled a reduction of dietary crude protein to the levels currently used. However, further reduction of dietary protein often results in poor performance. Several nutritional options have been investigated with a focus on crystalline essential and non-essential amino acids such as glycine. However, reducing the crude protein of meat-chicken diets does change the ingredient and nutrient profile aside from the amino acid composition. Alterations in non-protein nitrogen concentrations, dietary electrolyte balance, minerals, fibre and carbohydrates, methyl-donors and polyphenols must be considered in formulations to ensure successful implementation of reduced-protein diets. The ability to maintain performance with reduced-protein diets may benefit sustainability and longevity of the meat-chicken industry.</p>