Classical Treatment of Collisions Between Ions and Atoms or Molecules Classical Mechanics – Goal and First Results Classical Mechanics’ Approaches in Atomic Collisions Classical Treatment of Aq+ + H Collisions Classical Treatment of Aq+ + He Collisions Extension of CTMC Calculations to Multielectron Systems Collisions Aq+ + H2 Collisions of Aq+ and Multielectron Molecular Targets. Since the beginning of the twentieth century many experimental and theoretical works have been devoted to collisions between highly charged ions and atomic and molecular targets. It was realized that quantum mechanics is the only way a priori to describe such atomic phenomena. However since quantum mechanics is very difficult to apply for collision systems with more than two particles classical methods were very soon introduced and applied to simple collision systems and subsequently to more complicated systems. The results obtained by such classical methods were found to be surprisingly good and classical mechanics is now well established despite its approximations as a replacement for or competition with quantum mechanics in many cases. In this book the author will focus on the development of classical methods for describing collisional and post collisional processes. The results will be compared with those found using quantum mechanical models in order to demonstrate the ability of the classical approach to obtain many features and details of collision systems.