In recent years, a great variety of novel analytical methods has been developed to analyze composition, architecture and physico-chemical properties of microbial aggregates such as activated sludge flocs and biofilms. Simultaneously, new modeling approaches, aided by improved numerical simulation of the structure and function of these aggregates, have furthered our ability to understand their development and internal organization. The application of these novel analytical tools has led to fascinating discoveries, but at the same time has created a great deal of confusion in the engineering community. This volume is intended to bridge the gap that has emerged between science and engineering in the field of advanced biological wastewater treatment. Information is provided about methods which became available in recent years, both in microbiology and computer based modeling and simulation. Various authors elucidate the essence of the newly developed methods, the potentials these methods have in gaining better understanding of complex microbial systems, and the advantages which are envisioned with respect to optimization of biological wastewater treatment plants, trouble shooting and innovation.