As diesel emission regulations become more stringent, diesel particulate filters (DPFs) have become possibly the most important and complex diesel emission control device. This paper provides an update on the science and technology of diesel particulate emission control, drawing from the results of many research projects carried out by the authors in collaboration with the automotive industry and its suppliers. Both fundamental as well as application-oriented approaches are presented to study the physicochemical characteristics of diesel soot particles and soot deposits formed in DPFs, which are viewed as multifunctional separators/reactors. Theroretical and experimental aspects of filtration efficiency, pressure drop, ash accumulation and soot reactivity (with emphasis on catalyst-assisted soot oxidation) are addressed, employing systems ranging from small-scale filter samples to full-scale devices installed in the exhaust system of diesel engines. Properly combined, the current state of knowledge, experimental methods and simulation approaches all provide a rational and systematic route for enhancing the design and reliability of future diesel particulate emission control systems.