In the last few years heavy ion experiments have addressed key questions regarding the behavior of nuclear matter at high excitation and density. Simultaneous progress in theory has been achieved by the formulation of calculational tools to apply microscopic models to experimental observables. The present review covers a large part of this theoretical development. We provide enough details so that the uninitiated but interested reader can arrive at the present status of the theory and its relationship to current experiments. The energy range of interest here is 50 MeV/n lab to 1 GeV/n lab.