Cyanobacteria are the only prokaryotes which directly convert solar energy into biomass using oxygenic photosynthesis. Therefore, these bacteria are of interest for the production of biofuels, biotechnology and are of tremendous relevance for primary carbon fixation in many ecosystems. Mechanisms controlling gene expression cannot be understood entirely without information on the numbers and functions of regulatory RNAs. In cyanobacteria, non-coding RNAs have been characterized from simple unicellular species such as Prochlorococcus up to complex species such as Anabaena. Several of these RNAs function in the control of stress responses, photosynthesis, outer cell membrane protein biosynthesis and the differentiation of cells.