Abstract: Assessing the allergenic potential of transgenic proteins introduced into genetically engineered food remains a critical part of the overall safety assessment of these foods. Stability to digestion has been proposed as one of the steps in the decision tree approach to assess the allergenic potential of transgenic proteins. The validity of digestion stability as a criterion for protein allergenicity assessment, however, has encountered some criticism in recent years. This chapter gives an overview of the rationale behind the use of digestion stability as a criterion for protein allergenicity assessment and reviews the available data that may or may not support its use. The application of in vitro digestion assays for the assessment of allergenic potential of novel proteins and the factors that affect the assay results are also discussed. There is a need to establish standardized assay conditions so that direct comparison of results from different laboratories can be made. Consensus also needs to be reached on relating the measured digestibility to the allergenic potential of proteins.