At the most basic level, organic food is grown or raised without the use of synthetic chemicals. In the production of vegetables and fruits, no synthetic pesticides or fertilizers may be used, and no hormones or antibiotics may be used in the rearing of livestock or poultry. The concept of organic food, however, remains fuzzy. Beyond restricting the use of synthetic chemicals, other issues sometimes incorporated into the idea of organic food include: no sewage-sludge fertilizers, no food irradiation, no genetically modified organisms, humane conditions for livestock and poultry, sustainable land use practices, and just treatment of workers in the food production process.

Fresh tomatoes with a "No Pesticides" sign. Organic vegetables are grown without the chemical herbicides and pesticides used in conventional agriculture. (Nancy R. Cohen/Getty Images.)

Until the twentieth century, all human food was organic. At the dawn of World War II, the...