The use of energy transfer data and models in describing nonequilibrium polyatomic reaction systems is discussed with particular emphasis on the information needed for modeling vibrational energy transfer. In the discussion, it is pointed out that key areas of energy transfer knowledge are still lacking and the available experimental data are limited in scope and are of uneven quality. Despite these limitations, it is still possible to carry out meaningful simulations of chemical systems in which vibrational energy transfer is important. The vibrational energy master equation, which is the basis for modeling, and various experiments and calculations that provide the basis for practical energy transfer models and parametrizations are describ...