The biological control of weeds is receiving increased attention worldwide because it could help farmers reduce herbicide use. In this chapter, we review available knowledge on two biotic interactions that may lead to natural weed control, namely weed-sown plant interactions (competition, allelopathy) and weed-insect interactions (herbivory, granivory). We first provide a description of the processes at play and review available evidence of their effect on weed control, with quantitative estimates whenever possible. We then present available knowledge on the farming practices that can be mobilized to enhance these regulations. We conclude that weed-sown plant and weed-insect interactions can significantly affect weed growth and demography, and we show that some agricultural management options, whether implemented in arable fields, in field margins or at the landscape level, can promote biological weed control. We also identify some knowledge gaps that will require further research in the coming years.