Biosorption is an effective technology for the removal of organic and metallic elements, especially heavy metals from aqueous solution. Compared with conventional technologies for trace contaminant removal, such as chemical precipitation, evaporation, electroplating, adsorption and ion exchange, biosorption has advantages of high efficiency and low cost due to the economic biosorbent. Nowadays, a vast array of biomaterials have been tested as biosorbents including algae, fungi, yeast, wasted activated sludge, digested sludge, aerobic granules etc. Among these biosorbents, aerobic granules have more compact microbial structure than other loose bioflocs, so it is easier to be settled in the post treatment of biosorption. Biosorption indeed involves complex mechanisms of adsorption reaction, ion exchange reaction with functional groups on the cell surface, and surface complexation by extracellular polymeric substances. Thus far, intensive research has been dedicated to better understanding the mechanism of biosorption and its application in treating a wide variety of industrial waste-waters. Obviously, the basic research of biosorption has promoted this technology from laboratory-study all the way to the present pilot- and full-scale application, thus this book aims to provide all necessary basic knowledge of biosorption in terms of its fundamentals and main application.