Book excerpt: This book contains up-to-date information on the state of the art of research and applications in electro- and magnetorheology. A total of 130 papers are presented in four sections. The first section is devoted to the various applications of ER and MR fluids, like polishing, microfluidics, vibration control, robots, shock absorbers and dampers, MR and ER valves. The second part deals with the experimental characterization as well as the theoretical prediction of the mesostructure resulting from field-induced phase separation. The dynamics of phase separation is also included in this section. The third section is about the material properties; it includes papers on new compositions of ER or MR fluids, polymer blends, magneto- or electroactive elastomers and gels. The last section, about physical mechanisms, presents experiments and theories on the rheology of the fluids and its connection with microhydrodynamics and the structure of field-induced aggregates.