As simple photosynthetic organisms, microalgae can fix CO2 and syn­thesize organic compounds, such as lipids, proteins and carbohydrates in large amounts over short periods of time. Traditional methods of microal­gae cultivation based on photoautotrophic mode have many shortcomings, among which low cell density is a major issue giving rise to low produc­tivity, harvesting difficulty, associated high costs, and hence poor tech­no-economic performance. Therefore, a signficant effort towards com­mercializing microalgae biomass production is to develop high density cultivation processes. Two approaches are being actively researched and developed: (1) metabolic pathways control; (2) cultivation system design.