Chondroitin sulfate (CS) is the most abundant glycosaminoglycan (GAG) of the human body. Besides its natural occurrence as side chains in physiologically active proteoglycans localised at the extracellular matrices and/or at cell surfaces, this GAG can also be found in marine organisms with differential structures and functions, such as the anticoagulant fucosylated chondroitin sulphate isolated from sea-cucumbers. In addition, CSs isolated from vertebrate sources, such as shark and whale cartilages, are used as a biomedical ingredient for alternative medicinal therapies of osteoarthritis, osteoarthrosis, and possibly osteoporosis. CS formulations for oral administration are also employed as a nutraceutical to prevent lesions or degenerations of joint cartilages, especially in those people susceptible to physical impacts of their knees, like athletes, soccer players and dancers. In terms of structure, this GAG can show different sulfation patterns that vary accordingly with the types of cell, tissue, organism, and pathological conditions. However, the saccharide backbone of CS is always made up of alternating galactosamine and an uronic acid unit, regardless the source or condition. This book presents a compilation of some of the recent achievements obtained by scientific research on CS. Overall the most relevant areas and sub-areas regarding the science of this GAG type are somewhat discussed herein. The major areas include biology, biotechnology, physiology, chemistry and pharmacology. Specific sub-areas are biosynthesis, chemical and enzymatic modifications, extraction methods, occurrence and abundance, in vitro enzymatic degradations, structural diversity versus functions, disease-related mechanisms, physiological roles, medical applications, and novel methods of structural characterisation. The contributing authors of this publication are internationally recognised leaders in the field. All these features contribute significantly to the quality of this publication.