Herbicide resistance is by far the most common genetically modified trait in commercial agriculture.

Transgenic, herbicide resistant plants are part of a new weed control system. The system consists of a non-selective herbicide and a corresponding herbicide resistant crop:

•  A crop is made resistant to a particular herbicide. This is done by giving the crop a new gene or switching off an existing gene.
• The complementary herbicide is generally non-selective. It affects all sensitive plants by interrupting an essential metabolic activity.

Currently, two of these herbicide systems are commonly used: Roundup Ready (active ingredient: glyphosate) and LibertyLink (active ingredient: glufosinate).

Most herbicides used in conventional agriculture are "selective", meaning they only target certain plants. Conventionally, a specific combination of selective herbicides is needed for each crop.