Any discussion of vehicle compatibility represents an attempt to take an integrated approach pertaining to the numerous conflicts associated with goals related to passive vehicle safety. In order to keep the complexity of such a discussion within manageable limits, it would appear appropriate to concentrate on the most relevant collision modes. Compatibility characteristics are observed in vehicle crash testing. These must also be investigated in real-world accidents to verify their relevance to injury reduction. A list of relevant compatibility characteristics is given. Although, from a theoretical point of view, stiffness should be a dominating factor, it is difficult to find this in real-world accidents. A “bulkhead” concept is given as an attempt to avoid excessive crush of smaller vehicles by limiting the force level of the striking vehicle in frontal collisions. The demand for selfprotection, as defined by the barrier impact speed for which the vehicle is designed, limits the range of mass ratios, for which the bulkhead concept can be established. An over-view of ongoing compatibility research by automotive industry is given. One of the goals of this research is to classify vehicles compatibility by computer simulation, to the extent possible, and by vehicle crash testing, to the extent necessary.