Group 1 and group 2 sigma factors are sigma factors of bacterial RNA polymerase responsible for transcription from consensus-type promoters. Thus, these sigma factors form the framework for basic transcriptional regulation in bacteria. Cyanobacteria are known to have various group 2 sigma factors, typically more than 4, but only recently the particular function of each sigma factor is being elucidated. In response to environmental signals such as nutrients, light and temperature, cyanobacteria change their transcriptional profile first by activating specific transcription factors and subsequently by modifying the basic transcriptional machinery, which is often involved in the regulation of group 2 sigma factors. In this article, we give an overview of the composition and evolution of group 2 sigma factors in cyanobacteria and summarize what was presently revealed regarding their function.