This volume treats Cyanoprokaryotes with diversified thalli, with the typical presence of prominent, specialized cells having specific functions, complex life cycles, and a combination of various reproductive strategies. All heterocytous cyanobacteria are included, especially taxa studied and revised according to modern phylogenetic criteria. The author tried to respect all confirmed changes and corrections and to enable the identification of various populations in nature or in cultures according to morphological characteristics. A synthesis of modern results with traditional nomenclature is aimed to foster progress in cyanobacterial research and to enhance identification of natural populations using morphological criteria.