This review summarizes the microbiology and physiology of "Microthrix parvicella" and the methods of its growth control in activated sludge wastewater treatment plants. This filamentous bacterium is of high interest because of its worldwide involvement in severe bulking and foaming at wastewater treatment plants. We present a critical analysis of physiological and kinetic data on "M. parvicella" and discuss its growth and storage abilities in various environments with the aim of understanding the strategies of this organism to successfully compete with other bacteria in activated sludge. Additionally, this review elaborates on research needs for defining reliable control strategies of bulking and foaming based on key features of "M. parvicella".