The book is a venture in the field of Phycology revolving around the topic Extremophile cyanobacteria of Bhubaneswar and Puri, Odisha (India). The authors have made an attempt to isolate secondary metabolites of the sub-aerial cyanobacteria thriving in these two areas and exploit their potential in the field of biotechnology. The secondary metabolites of four sub-aerial cyanobacteria were extracted using various solvents and purified through column and thin layer chromatography followed by characterization using UV-vis and LC-MS spectroscopy. The structures of isolated compounds are 2, 4-Bis (2-methyl-2-propanyl) phenol - phosphorous acid, ergost-5-en-3-ol, 7, 11- dihydroxysolasodine and Iron(2+)amino (cyclopenta 2,4 diene-1-ylidine) methanolate 1,2,3,4,5-pentaphenycyclopenta-2.4,dien-1-ide. The compounds are also tested for antimicrobial activities against selected human pathogens and the findings are promising. The book will definitely provide a large scale information about sub-aerial cyanobacteria as potential source of secondary metabolites which could help further academicians and researchers toward possible application in the field of pharmacology.