Plants naturally produce numerous proteins and other compounds that deter or destroy pests and diseases. Although these protective components have always been present in plants, found in the food supply, and consumed by humans for many generations at some level in the diet, their induction and function are only now beginning to be understood by plant researchers. In addition, plants have recently been subjected to genetic manipulation involving the direct introduction of new protective traits that had never been a part of the food plant’s genetic complement. Both these types of protective traits, naturally occurring and introduced by genetic engineering, would be considered pesticidal under the pesticide definition found in U.S. law. The U.S. Environmental Protection Agency (EPA) has determined that the naturally occurring pesticidal protein present in all crop plants need not be regulated. They are specifically exempted from registration requirements because their safe use in food and feed, without causing side effects, has a considerable history.