This chapter summarizes the status, major challenges and potential contribution of microalgae-related wastewater treatment processes. Although the use of microalgae for wastewater treatment was proposed in the last century, technology was not sufficiently efficient and robust to be applied at a commercial scale. Only recent advances in the knowledge of biological systems, the engineering of reactors and the harvesting and processing of the produced biomass allow the development of the first industrial demonstrations. Facilities of several hectares are already in operation demonstrating the feasibility of this technology. However, challenges remain for the further improvement and enlargement of these systems. They are related to (1) the improvement of knowledge and management of biological systems, (2) the development of adequate strategies for the allocation and implementation of large-scale facilities, (3) the definition of optimal operation conditions including the development of non-assisted systems capable of operating under variable environmental conditions and (4) the development of adequate routes for the valorization of biomass. Much effort is being devoted to solving these challenges and thus making this technology reliable for industrial applications. Once it is achieved, the use of microalgae will be incorporated into the portfolio of available technologies for wastewater treatment. In this respect, no single technology is capable of solving all the scenarios related to wastewater treatment, but microalgae-related processes represent a semi-intensive technology capable of contributing to efficiently treating wastewater while recovering nutrient-energy-water scenarios related to temperate climates with no severe land restrictions. Moreover, the use of microalgae represents a change of paradigm in the field of wastewater treatment because by using this type of microorganisms it is possible to produce valuable biomass at a higher price than the wastewater treatment cost. The potential of microalgae-related wastewater treatment processes is thus highly relevant, and valuable to achieve the sustainable development goals defined by the United Nations.