Microalgae express high protein levels and can be produced in contained cultivation systems with low water requirements and complete fertilizer use. The production potential is 22–44 tons of protein per hectare per year although the current production scale is small. Techno economic analyses have shown good potential for scale-up and cost reduction. Large-scale production of microalgae in the post-fossil era will rely on the capture of carbon dioxide from the air, or sugars from crops. Microalgal amino acid composition matches well with requirements for food and feed, which, in combination with novel biomass pre-treatment steps, will guarantee high-quality microalgal protein. For a broadening of the microalgae species available as single-cell protein, novel food approval is required.