This reference book covers the ecological impact and biotechnological applications of diatoms. Diatoms contribute to 40% of primary productivity in aquatic ecosystems. They have a unique biomonitoring ability and sensitivity toward different pollutants in wastewater, and are thereby a tool for ecotoxicological monitoring. The book discusses the need for newer diatom-based indices for wastewater quality analysis. It describes the nutraceutical value of the myriad compounds like omega 3 fatty acids-DHA, polysaccharides, and phenols in diatoms. It also elaborates on the challenges in sustainable diatom biorefinery. This book is meant for microbiologists, biotechnologists, and marine biologists.