Several theories have been developed over the past 15 years to describe the ablation of a solid hydrogenic pellet injected into a hot plasma. The most widely accepted theory is the neutral gas shielding model. This model has been expanded to include ablation by fast ions (as well as electrons), realistic particle distribution functions, self-limiting ablation, and a cold ionized plasma shield beyond the ablating gas. Ablation measurements, including absolute pellet penetration and ablation profiles, from the Impurity Study Experiment, Poloidal Divertor Experiment, Doublet-III, Alcator-C, Tokamak Fontenay-aux-Roses, T-10, Texas Experimental Tokamak, Tokamak Fusion Test Reactor, and Joint European Torus experiments are compared with variations of the neutral gas shielding model under a range of input assumptions.