A two-stage approach to Diesel emission management in Diesel Hybrid Electric Vehicles is presented. The first aspect of this work focuses on a supervisory control strategy for charge-sustaining, parallel HEV drivetrains, which provides the a real-time control policy for the use of a CIDI engine and an electric motor, while simultaneous minimizing fuel consumption and reducing NOx emissions. Results show that only limited, although not negligible, gains in NOx emission levels can be achieved through the optimal control of the HEV drivetrain, necessitating an aggressive aftertreatment strategy. In the second facet of the work, an aftertreatment system is presented consisting of a set to parallel Lean NOx traps and a novel set of actuators for providing heat and hydrocarbons independent of the engine control strategy. The proper control of this system is obtained by a relatively simple dynamic model of the NOx absorbers, coupled with a real-time estimator of the NOx engine-out emissions based on the engine operating points (set by the control strategy) and their transient behavior. The system shows the potential to decrease NOx emissions by 90%.