Bacillus thuringiensis (Bt) maize genetically engineered for insect resistance has been commercially available in the United States since 1996. Bt maize has been popular with most U.S. growers because it provides economic advantages and reduces the reliance on chemical insecticides. Prior to commercialization all genetically-engineered (GE) crops go through a comprehensive and rigorous evaluation by three U.S. government agencies to demonstrate their safety to the environment and human and animal health. This paper focuses on improving methods to evaluate possible non-target effects of GE crops, which should be helpful to scientists in countries that are considering the use of GE crops.