Crops can be modified by engineering novel RNA interference (RNAi) pathways that create small RNA molecules to alter gene expression in crops or plant pests. RNAi can generate new crop quality traits or provide protection against insects, nematodes and pathogens without introducing new proteins into food and feed products. As a result, stakeholders and regulators need to construct credible ecological risk assessments (ERAs) that characterize potential exposure pathways and hazards for RNAi crops, including off-target effects, non-target effects and impacts from genetic mutations and polymorphisms. New methods are needed to identify RNAi crops and measure the environmental persistence of small RNAs. With some modifications, it seems likely that current ERA frameworks can be applied to most crops engineered through RNAi.