This book is based on the research work of the author, concluded in 1998. Work on algal floristics in India is of comparatively recent origin. The present work is the first comprehensive record of the blue-green algal flora of Alwar, a city in the northern Indian state of Rajasthan and its nearby places. The study has resulted not only in placing on record an appreciable number of known blue-green algae, but has also led to the discovery of nineteen new forms of blue-green algae.