The increasing global demand for energy and advances in new biofuel "production routes have increased the research on the potential of microalgae and cyanobacteria as a third generation of biofuels. The majority of research has been focused on using this type of biomass for producing biodiesel and biogas; however, more recent developments have indicated the potential of microalgae and cyanobacteria for the production of bioethanol. There are three routes for producing bioethanol from such microorganisms: the traditional one involving hydrolysis and fermentation of biomass with bacteria or yeast, the dark fermentation route, and the use of engineered cyanobacteria or "photofermentation." In recent years, the use of engineered cyanobacteria to directly produce ethanol has gained enormous attention, mainly after the successful use of these microorganisms in industrial plants. However, only little information is available on the efficiency and the real advantages and disadvantages of these processes, and particularly, a comparison between traditional processes and engineered cyanobacteria. This study compiles the main publications on the production of bioethanol from microalgae and cyanobacteria, and summarizes the main features, advantages, and key aspects for each type of process. The industrial implementation of these technologies depends on the capability of reducing production costs through more scientific research and technical development, to become competitive with the lower cost of fossil fuels also thanks to public subsidies. (C) 2016 Elsevier Ltd. All rights reserved.