The differential equations describing the thermochemical ablation-indepth process and the boundary layer transport processes which couple at the ablative surface are presented. Physical interpretations of the relationships are given along with the results of sensitivity analyses which pinpoint the properties of importance in ablation performance predictions. Char thermophysical properties are shown to have a considerable influence. Based on this observation, comparisons and discussion of recent ablative char thermal conductivity results are given for high-performance carbonphenolic and graphite-phenolic composites. Physical and chemical changes in the chars which influence the thermal transport properties are summarized and recommendations offered concerning the use of the information in ablation predictions. Finally, the important thermal and aerodynamic forces which may lead to thermomechanical and thermostructural erosion of the ablative are summarized.