  Collisions are a major modification process over the history of the Kuiper
Belt. Recent work illuminates the complex array of possible outcomes of
individual collisions onto porous, volatile bodies. The cumulative effects of
such collisions on the surface features, composition, and internal structure of
Kuiper Belt Objects are not yet known. In this chapter, we present the current
state of knowledge of the physics of cratering and disruptive collisions in KBO
analog materials. We summarize the evidence for a rich collisional history in
the Kuiper Belt and present the range possible physical modifications on
individual objects. The question of how well present day bodies represent
primordial planetesimals can be addressed through future studies of the coupled
physical and collisional evolution of Kuiper Belt Objects.
