Technical Abstract: Certain plant species are particularly well adapted to environments disturbed by humans. Often such species are invasive and problematic, and thus are classified as weeds. Despite our best efforts to control weeds, they continue to interfere with crop production. Clearly there is much to learn about weeds that could be used both to assist in their control, and to improve competitiveness in non-weedy species. In our ongoing efforts to control weeds, the tools of molecular biology have been enlisted; most apparent is in the development and commercialization of crop plants tailored to resist certain herbicides. Molecular biology also has been used to better understand how weeds compete and interact with neighboring plants, survive harsh environmental conditions, and evolve resistance to the herbicides being used to control them. The next generation of molecular biology tools, e.g., genomic resources, may yield novel weed control strategies and uncover new secrets about what makes plants weedy.