Аннотация:Cyanobacteria are an enormously diverse group of prokaryotes whose adaptive capacity along with the ability to tolerate extreme conditions makes them omnipresent. They are found in almost all the habitats of the Earth where life can be imagined to have flourished. Cyanobacteria are present in a wide range of habitats viz. marine, freshwater, soil, biological soil crusts, snow, cryoconites, etc. Further, they are found in symbiotic association with different hosts and also occur in extreme stressed conditions like volcanic ash, salted soils, and anthropogenically disturbed areas. This chapter explores the diversity of cyanobacteria from different habitats and enlists the dominant groups inhabiting these habitats. The diversity of cyanobacteria from different climatic zones; temperate, tropical as well as Polar Regions have been reviewed and documented in this chapter. The taxonomic complexity of cyanobacteria has hindered the capture of the actual biodiversity which is evident from the fact that the reported diversity encompasses only the traditional cyanobacterial genera. Morphological plasticity, ecological flexibility, and huge amount of heterogeneity are responsible for the confusions surfacing the cyanobacterial taxonomy. In this chapter, we also discuss the current trends in cyanobacterial taxonomy which would be essential in the studies conducted to capture the biodiversity of cyanobacteria from different habitats.