The development and validation of Computational Fluid Dynamic (CFD) models for diesel engine combustion and emissions is described. The complexity of diesel combustion requires simulations with many complex, interacting submodels in order to be successful. The review focuses on the current status of work at the University of Wisconsin Engine Research Center. The research program, which has been ongoing for over five years, has now reached the point where significant predictive capability is in place. A modified version of the KIVA code is used for the computations, with improved submodels for liquid breakup, drop distortion and drag, spray-wall impingement with rebounding, sliding and breaking-up drops, wall heat transfer with unsteadiness and compressibility, multistep kinetics ignition and laminar-turbulent characteristic time combustion models, Zeldovich NOx formation, and soot formation with Nagle-Strickland-Constable oxidation. The code also considers piston-cylinder-liner crevice flows and allows computations of the intake flow process in the realistic engine geometry with two moving intake valves. A multicomponent fuel vaporization model and a flamelet combustion model have also been implemented. Significant progress has been made using a modified RNG k-epsilon turbulence model. This turbulence model is capable of predicting the large-scale structures that are produced by the squish flows and generated by the spray. These flow structures have an important impact on the prediction of NOx formation since it is very sensitive to the local temperatures in the Model validation experiments have been performed using a single-cylinder version of a heavy duty truck engine that features state-of-the-art high-pressure electronic fuel injection and emissions instrumentation. In addition to cylinder pressure, heat release, and emissions measurements, combustion visualization experiments have been performed using an endoscope system that takes the place e of the exhaust valves.