Book excerpt: Hydrogels are made from a three-dimensional network of cross linked hydrophilic polymers or colloidal particles that contain a large fraction of water. In recent years, hydrogels have attracted significant attention for a variety of applications in biology and medicine. This has resulted in significant advances in the design and engineering of hydrogels to meet the needs of these applications. This handbook explores significant development of hydrogels from characterization and applications. Volume 1 covers state-of-art knowledge and techniques of fundamental aspects of hydrogel physics and chemistry with an eye on bioengineering applications. Volume 2 explores the use of hydrogels in the interdisciplinary field of tissue engineering. Lastly volume 3 focuses on two important aspects of hydrogels, that is, drug delivery and biosensing. Contains 50 colour pages.