Occupant motion is frequently studied to identify who was driving, occupant positions before collision, and the effect of safety belts. Identifying the driver is of particular interest in both civil and criminal cases resulting from vehicle collisions. The general methodology for studying occupant motion involves four basic steps: 1) inspect the vehicle interior for signs of contact between bodies and the interior, 2) obtain a thorough understanding of how the vehicles moved from first contact to maximum engagement to separation, 3) determine how bodies should have moved relative to the vehicle, and 4) review injury data and determine how injuries and interior vehicle contact points match. Vehicle inspection and occupant behavior assessment procedures are described for center, frontal, sideways, and rear collisions. A case study of a noncenter collision is presented, and vehicle collisions involving ejections and vehicle rollovers are discussed. The effect of restraint systems on occupant motion and injuries is considered. 47 figures, 7 references.