Managers must make effective use of cultural and biological methods of weed control in order to respond to increasing calls for reductions in herbicide and tillage use. Unfortunately, these methods are often of low and unreliable efficacy, only effective against low-density weed infestations and frequently permit considerable weed seed production. Therefore, use of cultural and biological methods must be supported by a concerted effort to reduce soil weed seed populations and prevent their long-term growth. Preventive weed management serves this purpose. However, scientific understanding of preventive management is limited and largely descriptive. Increased understanding of two major issues is needed: costs and risks associated with preventive practices must be quantified, and ecological mechanisms underlying preventive practices must be elucidated to determine how and why preventive practices affect weed populations. Promising avenues for basic and applied research in preventive weed management include: managing to increase mortality and limit dispersal of weed seeds and propagules, structuring farm operations in time and space to maximize preventive impact, and analyzing the functioning of existing preventive weed management systems. Production agriculture needs the support of a major research effort to improve preventive weed management.