For millennia, humans have been crossing strains of crops to make them healthier, hardier, and easier to cultivate. But the term "genetically modified organism" (GMO) typically refers to crops with a genetic code that has been altered in the lab. This often means that scientists are adding DNA from other organisms to make this crop better in some way—increasing the amount of food you can get from one plant in less time, making it more resistant to disease or extreme environmental conditions like frost or drought, or increasing its appeal to consumers by slowing the rate at which it spoils. In the past, scientists have made these genetic changes with two main tools, called zinc finger nucleases and TALENS. These enzymes are typically delivered into plant cells using a specially-designed virus or a gene gun, which bombards cells with the genetic material researchers are trying to add. And though these techniques work to alter a plant's genome, they're more expensive to create and more limited in where they can alter the genetic code than CRISPR.