This book presents the state-of-art marine metagenome research and explains the method of marine metagenomic analysis in an easy-to-understand manner. Changes in the marine environment due to global warming and pollution have become a major global problem. Maintaining a healthy marine ecosystem requires advanced environmental monitoring and assessment systems. As such, the book presents a novel metagenomic monitoring method, which has been developed for comprehensive analyses of the DNA of microorganisms living in seawater to further our understanding of the dynamics of the marine environment. The book can be used as a primer for new researchers and as a manual on experimental methods.