This book presents new and specific aspects in the field of polysaccharides and their derivatives recommended for use in medicine and pharmacy. At the same time the aspects developed in this book will be useful to design new systems for drugs delivery, immunomodulation, and new materials based on polysaccharides isolated from different sources and their derivatives. The structure and properties of polysaccharides from different sources with potential applications in the fields of medicine and pharmacy are discussed. Thus, the structural aspects concerning hyaluronic acids, fungal extra cellular polysaccharides, celluloses, alginates, hemicelluloses, dextran, glyconjugates and cyclodextrins are covered. The applications are described both for nonmodified and modified forms of polysaccharides for drug delivery, immunomodulation, tissue engineering and hydrogel preparation.