Recent laboratory research concerned with boundary layer, surface, and internal ablation mechanisms is examined, particularly in relation to their coupling with the imposed heating environment. Emphasis is devoted to defining ablator response at heating conditions representative of those encountered by the atmospheric entry of manned NASA vehicles. Experimental results are presented for four ablative composites (Teflon, phenolic nylon, epoxy-novolac, and silicone elastomer), which differ significantly in chemical formulation and mode of degradation. The influence of both test stream variables and chemical composition on material behavior is demonstrated and discussed. Future areas of ablation research are delineated by calculations that illustrate the relative importance of the various heat accommodation mechanisms available to a charring ablator at entry speeds above 15 km/sec.