Crops genetically engineered to express insecticidal proteins have been used in U.S. agriculture since 1996 and are being increasingly adopted worldwide. The ecological safety of these crops has been extensively considered by regulatory agencies prior to their commercial release, and is confirmed by a growing body of published research and experience under a variety of environments and management regimes. Ecological risk assessment provides a framework to understand the safety of these crops by considering the hazard potential of the expressed proteins in conjunction with environmentally relevant exposure scenarios. The ecological risk assessment framework applied to plant-expressed insecticidal proteins also provides insights into data and assessment requirements for forthcoming transgenic crops.