Although there are thousands of field trials conducted around the world each year (mostly in the US) on several dozen different genetically engineered (GE) crop plants, the vast majority of these are experimental in nature. Many of the field trials include GE plants developed for research purposes only, not necessarily with any intent to develop marketable GE varieties. Some GE varieties may be dropped during product testing or withdrawn in the process of regulatory approval.

Because it is difficult to predict which of these will make it to the market, the discussion of genetically engineered traits in this set of pages is limited to those GE crops which have been approved for commercialization in the US-- that is, all of the varieties which farmers are currently growing and which consumers may find on their plates today. Elsewhere, we will examine some of the other GE varieties being developed and which may be marketed in coming years.

There are 12 genetically engineered (GE) plant species that have been approved for commercial production in the US, and the traits that have been genetically engineered into them fall into six categories. Follow the links in the table to learn more about how each modification works.

Many of the most controversial modifications (and most frequently cited by activist groups) have never actually been marketed and are not available to consumers. Although many of them are real modifications that have been created in laboratories, and some even approved for experimental field trials, most of them may never reach the consumer. Here are a few examples, you may have heard of:

• tomatoes with fish antifreeze genes (unsuccessful)
• soybeans with Brazil nut allergens (never marketed)
• potatoes with snowdrop toxins (never marketed)
• rice that produces extra vitamin A (not yet submitted for regulatory approval)
• "Terminator" seeds that are sterile (will not be marketed)