Nonrelativistic Collisions.- First Order Considerations.- Considerations Beyond First Order Perturbation Theory.- Relativistic Collisions.- to Relativistic Collisions.- Descriptions of Collisions Within the First Order Approximation in the Projectile-Target Interaction.- Theoretical Methods Extending beyond the First Order Approximation.- Impact Parameter Dependence of Projectile-Electron Excitation and Loss in Relativistic Collisions.- Cross Sections...