This book summarizes the detail bio prospecting work done on Gelidiella acerosa, an agarophytes growing in the west coast and south east coast in India. The agar samples extracted from different Gelidiella acerosa samples were characterized and their respective qualities were assessed considering the application of the natural polymer in mind. The agar was also physically and chemically modified to yield materials having different properties, which may broaden the application opportunities. The results of systematic rheological investigations of agar under different chemical and physical environment is also included in this book. Apart from the work on agar, chemical modification of carrageenan and bio degradable film preparation from this polysaccharide is also discussed. A review article describing various chemical modifications so far carried out on polysaccharides is also part of the book.