NHTSA has initiated a research program to investigate the problem of aggressive or incompatible vehicles in multi-vehicle crashes. Collisions between cars and light trucks and vans are one specific. but growing. aspect of this larger problem. Light trucks and vans (LTVs) currently, account for over one-third of registered U.S. passenger vehicles. Yet, collisions between cars and LTVs account for over one half of all fatalities in light vehicle-to-vehicle crashes. In these crashes, 81 percent of the fatally-injured were occupants of the car. These statistics suggest that LTVs and passenger cars arc incompatible in traffic crashes. and that LTVs are the more aggressive of the two vehicle classes. The availability of newer safety countermeasures, e.g., air bags, appears to improve compatibility indirectly by improving the crashworthiness of later model vehicles. However, the fundamental incompatibility between cars and LTVs is observed even when the analysis is restricted to collisions between vehicles of model year 1990 or later -- indicating that the aggressivity of LTVs will persist even in future fleets. This paper presents an overview of results to date from this research program.