Technical Abstract: Lignin content of crop plants has been reduced using traditional plant breeding, natural and induced mutations, and insertion of transgenes. The effects of these genes and associated lower lignin content have been examined in terms of agricultural fitness or with regard to economically harvestable yields of useful plant products, or, in the case of some perennial species, survivability over multiple years. In general, crop yields are depressed by significant reductions in lignin content. Other negative effects observed in plants with lowered lignin contents include lodging and reduction of long-term survival of some perennial species. However, the interactions of genes involved in lignin metabolism with genetic background and the environment in which the low-lignin crop is cultivated are substantial. Examples are provided that demonstrate that lignin can be reduced in specific lines or populations without damaging fitness. It is concluded that it will be essential to incorporate lignin reducing genes into numerous genetic backgrounds and combinations, and evaluate the resulting lines in diverse environments, in order to discover optimal combinations and to obtain a true measure of value and fitness in agricultural systems.