The algae are considered GOLD LEVEL organisms owing to their wide applicability and easy growth in less stringent conditions. These organisms have been present on earth since billions of years long and played crucial role in planet's ecosystems. This book provides information on the aspects of algae from their origin and classification to their cellular structure and ecological dynamics. The book also gives understanding to their applicability in genetic engineering, biofuel production, dye decolorisation and nutrients supplement so as to make them sustainable solutions for the environmental problems. Thus, providing a read through its natural environment and biotechnological application.