Microalgae use sunlight to produce TAGs and starch, and their biomass productivity greatly exceeds the best producing crops. In addition, some of the microalgae are also capable of producing hydrogen-a fuel that liberates a large amount of energy per unit mass. Microalgae biofuel can be produced on nonarable land, using for this purpose saline and wastewater streams. In this way the production of biofuel by algae will allow arable land to remain available for cultivation of crops, thus avoiding the adverse impacts on food supplies. For these features, microalgae have been considered a promising platform to produce of biofuels. However, it is of critical economic importance-for the practical use of microalgae as source of renewable energy, to achieve a significant improvement in the efficiency of biofuel production. Nowadays, with genome sequence data and a wide variety of genetic tools and powerful analytical techniques available, new genetic engineering modifications can be accomplished to exploit marine algae as efficient sources of biofuels if protocols for chloroplast and nuclear transformations, and stable expression of genes are developed for species of interest. Such modifications might include accurate reprogramming and manipulation of metabolic pathways, combined with strategies to overcome the limitations of CO2 fixation and light capture, which are crucial to optimize biomass productivity.