Transgenic glufosinate- and glyphosate-resistant crops are currently commercialized, and bromoxynil- resistant crops have been removed from the market for economic reasons. Glyphosateresistant cotton and soybean have become dominant in those countries where they have been approved for planting. Potential effects of glufosinate and glyphosate on contamination of soil, water and air are minimal, compared to those caused by the herbicides that they replace when herbicide-resistant crops (HRCs) are adopted. No risks have been found with food or feed safety or nutritional value in products from currently available HRCs. Both glufosinate- and glyphosateresistant crops promote the adoption of reduced- or no-tillage agriculture, reducing environmental degradation by agriculture. HRCs have caused evolution of herbicide resistance in weed species and shifts to those species that are naturally resistant. Transgene flow with HRCs is a concern for commercial and ecological reasons. In canola, rice and bentgrass, herbicide resistance transgenes have been found in fields that are supposed to be non-transgenic. Under some circumstances, transgene flow (introgression) to plants that might become problems in natural ecosystems remains the largest risk of HRCs.