This book describes mixed classical and quantum theories of dynamical processes with a particular emphasis on molecular collisions. Purely quantum or purely classical approaches are inadequate for many systems. The quantum classical theory is important to conduct practical calculations involving reactions and dynamics of molecules in the gas phase, in solution, and on surfaces. This book presents not only the theoretical background but also the actual working equations in great detail. It will meet the needs of a growing number of chemists today who are interested in theoretical simulation.