Technical Abstract: Herbicides with new modes of action are badly needed to manage evolution of resistance of weeds to existing herbicides. Yet, no major new mode of action has been introduced to the market place for about 20 years. There are probably several reasons for this. New potential products may have remained dormant due to concerns that glyphosate-resistant (GR) crops have reduced the market for a new herbicide. The capture of a large fraction of the herbicide market by glyphosate with GR crops led to significantly diminished herbicide discovery efforts. Some of the reduced herbicide discovery research was also due to company consolidations. There could be other economic concerns and/or problems with toxicology with some potential products also. Another problem might be that the best herbicide molecular target sites may have already been discovered. However, target sites that are not utilized, for which there are inhibitors that are highly effective at killing plants, suggests that this is not true. Results of modern methods of target site discovery (e.g., gene knock out methods) are mostly not public. These methods have limitations that are discussed. In summary, the reasons for a long dry period for new herbicide target sites are unclear, but several factors are probably involved. The economic stimulus to the herbicide industry caused by the evolution of herbicide-resistant weeds, especially GR weeds, may result in one or more new modes of action becoming available in the not too distant future.