The high quantities of protein - up to half of their weight - make algae one of the most interesting emerging food sources. Algae are simple, single-cell organisms that can grow very rapidly at sea, in polluted water and in places that would normally not generate food crops, ranging from giant seaweeds and kelps to microscopic slimes. Algae would be a cost-effective, land-and climate-neutral alternative to meat proteins while at the same time fixing large amounts of C02 from the atmosphere.