The increase in carbon dioxide (CO2) emissions to the atmosphere is provoking an environmental crisis, as CO2 is considered the main responsible for the greenhouse effect and, consequently, global warming. The constant search for effective systems to capture CO2 has revealed the potential of microalgal cultures to perform this task. Microalgae are photosynthetic microrganisms able to uptake CO2 from both the atmosphere and flue gas emissions, converting it into biomass or other organic compounds. One important advantage of microalgae is that they present higher specific growth rates and biomass productivities than other photosynthetic organisms, such as terrestrial plants. This chapter presents an overview of the main studies aiming to evaluate the performance of microalgae for CO2 capture from the atmosphere or flue gas emissions. Also, the main limitations of using these microrganisms are described, highlighting the main research needs. (c) 2020 Elsevier Inc. All rights reserved.