While the nutritional profiles of microalgae vary considerably with the species used, a large majority are characterised by protein, carbohydrate, and lipid contents that are comparable, if not superior, to conventional feedstuffs. Dietary soybean meal typically contains up to 48% crude protein, and lays claim to a relatively well balanced amino acid profile. The diversity of microalgae makes certain species amenable to cultivation for diet-specific needs of humans and animals. A commonly cultivated algae species for human consumption: S. maxima, contains high levels of vitamin B1, vitamin B2, and β-carotene, and up to 71% crude protein with sufficient concentrations of all essential amino acids except for the sulfur-containing ones. Since protein is considered to be the most expensive nutrient in animal feed, developing natural alternatives to soybean meal may be cost competitive. Among all dietary amino acids, lysine and methionine are the first and second limiting amino acids. Many microalgal species contain relatively high amounts of lysine, but are somewhat deficient in the sulfur-containing amino acids: cysteine and methionine. To maximise amino acid utilisation by animals, diets are typically formulated by mixing different feedstuffs to balance amino acid profiles and (or) by supplementing synthetic amino acids to meet their nutrient requirements.