CONTENTS:- 1. Introduction to the Algae and its Occurrence. 2. Roles of Algae in Biogeochemistry. 3. Introduction to Algae Biofuels. 4. Algae in Oil and Hydrogen Production. 5. Algae in Biotec Associations. 6. Origin of Eukaryotic Algae. 7. Green Algae. 8. Algae and aquatic Weed Control. 9. Red Algae. 10. The Brown Algae. 11. Phytoplankton Ecology.