The book presents discussions on: Biology and ecology of major troublesome weeds infesting rice, wheat, corn, soybean, focusing on different cropping patterns in both tropical and temperate cropping systems and science-based weed management practices involving chemical, non-chemical, biological, integrated methods.; and Herbicides used, with their most recent classification, identification of new target sites, mechanisms and modes of action and how and why weeds evolve resistance to herbicides. New concepts, new paradigms and new technologies to manage evolution of resistance to herbicides including weed genomics, bioherbicides and allelochemicals.