Bt corn is a variant of maize, genetically altered to express the bacterial Bt toxin, which is poisonous to insect pests. In the case of corn, the pest is the European Corn Borer.  Bt-corn is a type of genetically modified organism, termed GMO. A GMO is a plant or animal that has been genetically modified through the addition of a small amount of genetic material from other organisms through molecular techniques. Currently, the GMOs on the market today have been given genetic traits to provide protection from pests, tolerance to pesticides, or improve its quality. Examples of GMO field crops include Bt-potatoes, Bt-corn, Bt-sweet corn, Roundup Ready soybeans, Roundup Ready Corn, and Liberty Link corn.

Expressing the toxin was achieved by inserting a gene from the soil-dwelling microorganism Bacillus thuringiensis into the corn genome. This gene codes for a toxin that will crystallize in the digestive tract of insect larvae, leading to its starvation.

Genetically modified foods are foods derived from GMO crops. For example, corn produced through biotechnology is being used in many familiar foods, including corn meal and tortilla chips. In addition, corn is used to make high fructose corn syrup, which is used as a sweetener in many foods such as soft drinks and baked goods. While the FDA (U.S. Food and Drug Administration) regulates genetically modified foods, it considers Bt-corn to be nutritionally equivalent to traditional corn.

In 2001, Bt176 varieties were voluntarily withdrawn from the list of approved varieties by the Environmental Protection Agency when it was found to have little or no Bt expression in the ears and was not found to be effective against second generation corn borers. This status was updated in 2005.

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