Since its commercial introduction in 1974, glyphosate [N-(phosphonomethyl)glycine] has become the dominant herbicide worldwide.  There are several reasons for its success.  Glyphosate is a highly effective broad-spectrum herbicide, yet it is very toxicologically and environmentally safe.  Glyphosate translocates well, and its action is slow enough to take advantage of this.  Glyphosate is the only herbicide that targets 5-enolpyruvyl-shikimate-3-phosphate synthase (EPSPS), so there are no competing herbicide analogs or classes.  Since glyphosate became a generic compound, its cost has dropped dramatically.  Perhaps the most important aspect of the success of glyphosate has been the introduction of transgenic, glyphosate-resistant crops in 1996.  Almost 90% of all transgenic crops grown worldwide are glyphosate resistant, and the adoption of these crops is increasing at a steady pace.  Glyphosate/glyphosate-resistant crop weed management offers significant environmental and other benefits over the technologies that it replaces.  The use of this virtually ideal herbicide is now being threatened by the evolution of glyphosate-resistant weeds.  Adoption of resistance management practices will be required to maintain the benefits of glyphosate technologies for future generations.