The great controversy over the use of agricultural crops as a source of energy is well known – fundamentally due to its possible competition with crops for food. The use of sources of an organic nature for the production of biofuels, different from the traditional use for crops, could be the solution to the social debate that has arisen in this sector. As a consequence, it has been necessary to turn to alternative resources to traditional crops, such as lignocellulosic biomass and/or microorganisms, amongst these being microalgae. In concrete, the mass production of microalgae could meet this demand given that it does not compete with the food sector, does not require large surface areas nor fertile terrain and maximises water savings (closed cycle) for their production. At the same time, it contributes to environmental enhancement with CO2 capture and can be integrated into the use of saline industrial effluents. The Energy Unit at TECNALIA is researching the potential of mass production of microalgae as a crop, working on the selection of stocks, the optimisation of crop production systems (open, closed and mixed), as well as the optimisation of various operation variables in the harvesting and final treatment of the microalgae for their transformation into energy. At the same time, the synergic aspects of the process are being studied, such a the capture of CO2 as a nutrient for the algae, the use of saline industrial effluents and the valuation of sub-products. Basically what is involved is achieving the mass production of microalgae as precursors of biomass and/or bio-oils. To this end, a number of technological fields have to be developed, such as genomics and the selection of stocks that are the most productive and resistant to external agents; studying the crop parameters and nutrients most suited to the growth of microalgae, and especially the role of CO2; using open crop systems (raceways) and closed ones (photobioreactors), or mixed systems (raceways with greenhouse). The goal is to achieve great rates of productivity at low operational costs and investment, at the same time as studying the application of the best technologies available for harvesting and treating the microalgae crop in large, liquid-medium volumes until achieving the dry biomass itself or the bio-oils extracted from the microalgae are obtained at reasonable prices and which can be potentially used to produce energy and/or biofuels. Microalgae and its viability as a source of energy from biomass for energy use or by transformation into biofuels, is a field still in the research stage but with interesting perspectives for the future. For the moment, the complete process has not yet been sufficiently developed at an industrial level to be exploited by industries in the sector and the viability of its application has not been adequately demonstrated despite certain publicity by companies without any technological foundation. More exhaustive studies are required and the crop has to be planted on a large scale in order to explore the viability in the domain of energy. For the moment, research is focused on developing viable processes and evaluating possible applications of interest to the industrial sector.