Some algae, particularly blue-green and green algae, contain very high levels of protein, typically 40 to 60% (of dry matter), that can be used as functional food ingredients. Algal proteins possess a high nutritional value in terms of protein content, amino acid quality and nutritional acceptability. Their functional properties, such as gelation, water and fat absorption capacity, emulsification capacity, foaming capacity, etc., are also comparable with those of terrestrial plants. Besides their natural character, other important aspects related to the algal proteins are their easy cultivation, their rapid growth and the possibility to control the production of some specific compounds by manipulating the cultivation conditions. Algal proteins possess a great economic potential for use in functional, processed foods and health foods.