The cyanobacteria are characterized by a photoautotrophic mode of life. They generally perform oxygenic photosynthesis in intracellular membranes, the thylakoids, and fix CO2 with the aid of a CO2 concentrating mechanism including the carboxysome. As nitrogen sources they can generally use nitrate or ammonium ions but many strains can also fix atmospheric nitrogen. Notwithstanding a photoautotrophic lifestyle, the cyanobacteria show an astonishing morphological diversity, presenting different modes of cell division (including binary and multiple fission) and different supracellular organizations. Whereas some cyanobacteria are unicellular, others grow as chains of cells termed trichomes or filaments. Among filamentous cyanobacteria, some exhibit different developmental processes producing structures for dispersal (hormogonia), resting cells (akinetes) or cells specialized for a metabolic function (the N2-fixing heterocysts).

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