Book excerpt: From the Authors' Preface The advances made in the area of controlled drug delivery during the last two decades are remarkable ....Of the many polymeric materials, biodegradable hydrogels present unique advantages and opportunities in the development of ...delivery devices....We have undertaken the challenge of putting together information relevant to biodegradable hydrogels in one place. This book covers the mechanisms of biodegradation, types of biodegradable hydrogels,chemical and physical gels, chemical and enzymatic degradation, and examples of biodegradable drug delivery systems.