The world's future energy demand calls for a sustainable alternative for the use of fossil fuels, to restrict further global warming. Harvesting solar energy via photosynthesis is one of Nature's remarkable achievements. Existing technologies exploit this process for energy 'production' via processing of, for example, part of plant biomass into ethanol, and of algal biomass into biodiesel. Fortifying photosynthetic organisms with the ability to produce biofuels directly would bypass the need to synthesize all the complex chemicals of 'biomass'. A promising way to achieve this is to redirect cyanobacterial intermediary metabolism by channeling (Calvin cycle) intermediates into fermentative metabolic pathways. This review describes this approach via the biosynthesis of fermentation end products, like alcohols and hydrogen, driven by solar energy, from water (and CO2).