Contents: Preface. Introduction. 1. Biology of blue-green algae (Cyanobacteria). 2. Isolation, purification and cultivation of blue-green algae. 3. Taxonomic enumeration of rice-fields blue-green algae. 4. Importance of blue-green algae. Bibliography. Glossary. Index. Rice fields provide an ideal environment for harbouring Cyanobacteria (blue-green algae). A number of reports are now available to indicate a wide distributional spectrum of these organisms under different soil and agro-climatic conditions. There is enough evidence that these rice fields cyanobacteria are capable of atmospheric nitrogen fixation in considerably large quantities and to some extent the organic matters. Thus the role of nitrogen fixing Cyanobacteria in the maintenance of the rice field soil fertility has been well sustained and documented. There is now positive evidence for the nitrogen fixing ability of more than 100 species of Cyanobacteria. During growth, Cyanobacteria liberate relatively large quantities of combined nitrogen mainly in the form of polypeptides with lesser amounts of free amino acids. Vitamins and auxin live substance. Approximately 40 to 50% of the algal nitrogen has been found to be recovered by the rice crop. These observations indicate the efficiency of these organisms as a biological nitrogen source in a rice field ecosystem. In this book, a comprehensive floristic account on the rice field Cyanobacterial studies were attempted. In addition this book also offers an extensive discussion on isolation and cultural techniques and application in various fields.