Three-dimensional (3D, or nonplanar) changes in velocity occur in collisions between rough bodies if the configuration is not collinear and the initial direction of sliding is not in-plane with two of the three principal axes of inertia for each body. In collisions between rough bodies, dry friction can be represented by Coulomb's law. If there is a tangential component of relative velocity at the contact point (sliding contact) this law relates the normal and tangential components of contact force by a coefficient of limiting friction. The friction force acts in a direction opposed to sliding. For a collision with planar changes in velocity, sliding is in either one direction or the other on the common tangent plane. In general however, friction results in nonplanar changes in velocity. Nonplanar velocity changes give a direction of sliding that continuously changes, or swerves, during an initial phase of contact in an eccentric impact configuration. This chapter obtains changes in relative velocity during rigid body collisions as a function of the impulse P due to the normal component of the reaction force. The changes in velocity depend on two independent material parameters – the coefficient of friction and an energetic coefficient of restitution.