The commercial production of microalgae started in the early 1950’s. Especially in the last two decades, these amounts have tremendously increased. In view of growing world population and limited fossil fuels, microalgae are seen as one promising alternative source for biofuels and high value products (like proteins and ω-3 fatty acids) in different industry branches (e.g. food, feed, cosmetic and pharmaceutic products or waste water treatment). Currently, they are mainly used for food and food supplements. The potential of the small photosynthetic microorganisms for other applications were proven in lab scale experiments. There are obstacles as high processing costs, low production yields and production stability which continue to prevent the commercial use. Furthermore, without artificial lighting and heating, the production in Europe is limited from March to October. As a result, the market prices are often the bottle neck in order to sell products. There is a need for the optimisation of the processes and reactors (e.g. important growth factors, selection of microalgae species and design) to tap the full potential of the green cell factories.