This chapter provides a scientific foundation for subsequent loadcase chapters as well as a foundation of loadcase terminology. Collision physics will be introduced and the chapter material will build to the construction of a general collision model. It is important to note that the goal of this chapter is not only the derivation of equations. Of equal importance is the reader’s development of intuition with regards to collisions and the physics that governs automotive structure, and the information is presented in a way to encourage such development.