In the current era of herbicide-based weed management systems, it is easy to assume the success of weed management is based solely on appropriate selection and application of herbicides. However, many factors place selection pressures on weeds, and these subtle influences may determine the long-term success or failure of a weed control program. As farmers manage more acres with less equipment and manpower, it will become increasingly important to take advantage of any and all available tactics that can help maintain the effectiveness of modern herbicides. This paper will provide a brief overview of some of the less obvious factors that regulate weed communities in agronomic fields.