Microalgae are photosynthetic microorganisms that can reach higher areal productivity than terrestrial plants, do not require arable land or fresh water, and can use fertilizers with almost 100% efficiency. Microalgae-derived products are therefore considered a promising sustainable source of food and other commodities.Microalgae are commonly grown exploiting their photoautotrophic capacity (henceforth referred to as autotrophic), in which cells harvest light energy, use CO2 as a carbon source, and release O2 as a byproduct. CO2 and aeration are provided to prevent carbon limitation and oxygen accumulation. Some microalgae can also be grown heterotrophically, in which organic carbons, such as sugars and organic acids, are used as carbon sources in the absence of light. In this trophic mode, O2 is consumed and CO2 is released as a by-product. Autotrophic and heterotrophic cultivation of microalgae can be combined in mixotrophic cultivation in which light and reduced organic carbons are simultaneously exploited within a single microalgal monoculture.In this thesis we designed a novel mixotrophic process called “oxygen balanced mixotrophy” in which there is no net O2 production. This was possible by tuning the supply of organic carbon to the rate of photosynthesis. When illuminated, the culture did not required any aeration. Due to the internal gas recirculation, about the 90% of the organic carbon provided was converted into biomass making the process almost carbon neutral. The presence of two complementary growth modes within a microalgal monoculture led to doubled biomass productivity and concentration in comparison with an autotrophic reference.Oxygen balanced mixotrophy has been successfully applied to with two industrially relevant microalgal strains: Chlorella sorokiniana and Galdieria sulphuraria. G. sulphuraria had a protein content of over 60% w/w and compared favorably with the FAO dietary requirements for adults regarding amino acid composition. Moreover G. sulphuraria contains a high proportion of sulphurated amino acids compared with Chlorella, Spirulina and soybean protein. Due to its attractive amino acid profile and high protein content, G. sulphuraria proved to be a good candidate for food and feed applications to overcome sulphurated amino acid deficiencies.Mixotrophic cultivation of G. sulphuraria demonstrate to be also a good strategy to produce the blue pigment phycocyanin with superior acid- and thermal stability compared to phycocyanin extracted in Spirulina.Finally the insights of this thesis were combined in a techno-economic model. Projections were made on biomass production costs for a hypothetical 100-hectare facility located in southern Spain. Our projections indicated that mixotrophic cultivation of Chlorella sorokiniana would half microalgal production cost mainly due to the doubling of biomass productivity under mixotrophy. For Galdieria sulphuraria, because of the expected low efficiency of CO2 uptake and the doubling of biomass productivity, mixotrophic biomass production costs would be three times cheaper than autotrophic production. Microalgal protein yield per hectare is expected to be 30-60 times higher than for soy beans while it would require 25-50 times less water. If glucose is used as a substrate for mixotrophic cultivation, the land and water consumption of sugar production substantially increases the overall water and land usage. However, when we consider the land and the water needed for sugar beet production, mixotrophic cultivation still requires 4 times less land and 7 times less water than soy beans. Altogether, this thesis successfully designed and applied oxygen balanced mixotrophy with two industrially relevant microalgal strains proving its effectiveness in reducing microalgal production costs. We are on the right track to achieve an economically feasible protein production from microalgae for food and feed purposes.