A quantitative model for gettering processes is presented. First, lifetime-killing impurities that are fixed in the silicon lattice, either as precipitates, trapped atoms, or substitutionals, must he extracted. Then they travel as interstitials to a sink region where they cease to be harmful to the electron device behavior. The model is applied to several cases where aluminum or phosphorus gettering is performed. Agreement with experimental results commonly observed is found, and several interesting conclusions are reached. Application to a more complex situation provides a way of identifying the phenomena involved and their importance. This quantitative model is thought to be a useful tool for the interpretation of gettering experiments.